OK this is gonna be long.
1. The popular voteSomebody has helpfully put the popular vote tallies on Wikipedia already.
Geographical Constituencies = 35 seats elected by regular voters
Functional Constituencies = 30 seats elected by special interest groups, so no popular vote.
District Council Superseats = 5 seats elected by a hybrid method. Candidates consist of district councilors (the lowest level of local government) who are nominated by their fellow councilors, and then put up to the popular vote.
In 2012:
The democratic camp won 56% of the popular vote in the geographic constituencies and 18 seats.
The pro-government side won 43% of the vote and 17 seats.
Non-aligned independents won 1% of the vote and 0 seats.
The democratic camp constituencies won 6 functional constituency seats
The pro-government side won 24 functional constituency seats
The democratic camp won 51% of the popular vote for the DC Superseats, and got 3 seats
The pro-government side got 45% of the popular vote, and 2 seats.
Non-aligned independents won 4% of the vote, and 0 seats.
In 2016:
In the geographical constituencies, old-school democrats won 36% of the popular vote while localists won 19%, making a total of 55% of the popular vote. They got 13 and 6 seats respectively, so 19 seats total.
The pro-government side got 40% of the popular vote and 16 seats.
Non-aligned independents got 4% of the vote, and 0 seats.
In the functional constituencies, the democrats got 7 seats.
The pro-government side got 22 seats.
A non-aligned independent (democratic leaning) got 1 seat. (This seat - architecture, surveying and planning - traditionally goes to the government side.)
In the DC superseats, the democrats got 58% of the popular vote, and 3 seats.
The pro-government side got 42% of the popular vote, and 2 seats.
As you can see, the democrats didn't really improve their vote share. It took a massive turnout just to counter the granny-busing tactics of the government side. However, they used their votes more efficiently, and in doing so clawed out 1 more geographical seat by a narrow margin. They also blundered a bit and had a couple of narrow losses, so they could've won even more. The architecture seat contains a mixture of human and corporate voters, so it can be flipped with difficulty, and this time they pulled it off. The doctors also flipped back to the democratic side too.
2. Factional splits in the pro-government side Yes, there are splits in the pro-government side, but it's hard to know what's going on and who's aligned with what, exactly. It's muddied by the fact that the pro-government side had created several flavours of loyalist to appeal to different segments of the conservative electorate, but the differences between them are more marketing than real. As best as I can tell, the factions consist of:
a) The Tycoons. Originally loyal to the Brits, they switched sides when China came to get its colony back. While they used to be trusted to run Hong Kong, they have fallen out of favour with Beijing due to their own incompetence and corruption. They openly despise the current Chief Executive, CY Leung, partly for not being pro-business enough (think Jeb Bush Republican vs. Grover Norquist Republican), and partly for being a douche. His personality doesn't have much to recommend.
b) Rural Kingpins. They are the self-proclaimed leaders of the indigenous villagers, people descended from families that were farming here before the arrival of the British. The rural kingpins own vast holdings of land and collude with real estate developers and government for fun and profit. They are nasty pieces of work with ties to organized crime, and were recruited to the loyalist side as muscle. They seem to have their own internal splits, and the candidate who was intimidated into quitting was one rural leader drummed out by another who had secured the backing of the Chinese government.
c) Patriotic Hawks (?) Aligned with current Chief Executive, CY Leung. It's hard to say who these people are exactly, since their public side seems to consist of important people you've never heard of popping out of the woodwork at opportune times to rant about traitors and splittists and CIA plots and how the localists are breaking the law just by existing. I do not know which faction of the Chinese government they are aligned with - whether they are taking orders straight from President Xi Jinping, or whether they're some other faction trying to puff themselves up.
d) Old School Leftists/Patriotic Doves (?) The old school leftists were loyal patriotic communist sympathizers since the 1950s. Shunned under British rule, they were elevated to positions of power when China took the place back in 1997. However, they were always given supporting roles, and never allowed to be in charge. Some of them seem to genuinely care about the welfare of the people, which sets them apart from all the other loyalist factions. They don't like CY Leung and have obliquely criticised his hardline approach for exacerbating tensions. It's hard to tell whether it's just a good cop/bad cop act, or if they have the backing of another faction high up.
e) Bureaucrats. The old British-trained civil service. They're closer to the tycoons than anybody else, especially those in the powerful real estate business. Motivated by careerism and profit, top civil servants have struggled to win the trust of Beijing. They were briefly on top from 2005-12 when career civil servant Donald Tsang became chief executive, but he and his 2nd in command fell to corruption charges. Down the ranks, the civil servants mostly want to protect their (substantial) paychecks and avoid controversy. Individually there are some civil servants who want to do good things for the community, but as an institution, they're rigid and narrow-minded.
3. Can the radicals do anything?As legislators, they have limited powers. The legislative council was set up to make it hard for legislators to propose bills, so legislators can only question government policies in committees and vote on government-proposed legislation. They can filibuster. Their only power is being the biggest pain in the arse to the government as possible, a role the radicals seem happy to fulfill.
But this is not why Beijing is freaking out. They are freaking out because until last year,
we had no independence movement. It was a beyond a fringe idea. They are exceedingly jumpy about the idea of independence because they have Tibet, Xinjiang and Taiwan(1) wanting to fly off too, and they consider that a grave threat to China's territorial integrity and national security.
Especially since some of the more radical radicals have publicly stated that they are not averse to using violence (2) to achieve their aims, the hardline faction portrays them as a bunch of terrorists.
They're probably also alarmed by the fact that there is strong support for the radicals among people aged 18-29. They've lost a whole generation. They were hoping that young people born after the Handover would grow up to be patriots, and the democrats would age themselves out. Nope.
(1) Taiwan's been a de-facto separate country since 1949, but they won't admit it.
(2) By which they mean rioting. There aren't any guns here.