I'm
terrible at people-searching, but here's a start.

Olivia mentions living with Liz & his husband in Somerville, Massachusetts.
(For those unaware, this is essentially Boston.)

On Liz's old blog, he partially attributed his move to Boston to an XKCD meetup.
https://archive.ph/C6ZlP

Liz actually gives the address of the home he bought, in a blogpost dated December 20th, 2009:
https://archive.is/8VFLc
Somerville and Cambridge seemed like an ideal match for me – Aunt Eleanor just half an hour away, friends within walking distance, dense dog-friendly public transit and the ability to leave the car commute behind, median home prices 60% those of the Bay Area, MIT right across the street from the office… and I also found
a house within my affordability range that I fell in love with at first sight.
That link goes to this house:
https://www.redfin.com/MA/Somerville/62-Albion-St-02143/home/8710469
62 Albion St, Somerville, MA 02143
It was sold in October 2009, which lines up with the December 2009 blogpost above. Btw, Liz bought it for $435k (that Google money must have been very nice...), and the house is now worth $1.2 mil. I believe Liz still owns it, since there's no record of it being sold again.
So now we know where Liz was living during his time in Boston. How about Randall Munroe?
This is trickier, but a basic search turns this up:
https://www.fastpeoplesearch.com/name/randall-munroe_massachusetts
(Appears to be the same Randall Munroe based on the info in
his Wiki article.)

Hmm, no exact matches. However,
256 Summer St, Somerville MA 02143 is
very close to Liz's address. Only 0.6 miles away.
Looking closer at what Olivia said again:
lived 2 her&wife in somerville ma soon after they got married (was a whole group there at that time connected to xkcd, randall lived there. his.. trans sister? was over at some point)
I'm wondering if he meant that Randall Munroe was living in the same area. ("There" = Somerville, MA. Not necessarily in Liz's house.) Or maybe Randall just spent a lot of time over at Liz's house? Hard to say. ¯\_(ツ)_/¯
Hopefully better sleuths than me can turn up more.
In regards to the alleged troon brother, this old article from 2009 mentions that Randall has two younger brothers ("Doug and Ricky"):
https://richmondmagazine.com/news/a-cartoonists-mind-11-24-2009/
Crum notes that Munroe's younger brothers, Ricky and Doug, are also interested in math and science.
It's possible that one of them trooned out, but I have no evidence for this (yet).
Fastpeoplesearch lists a Douglas Munroe and a Richard Munroe associated with Randall, and they're the right ages (34 & 37) to be his (39) younger brothers:
https://www.fastpeoplesearch.com/name/randall-munroe_massachusetts

More digging needed.
Something else interesting from Liz's old blog, posted in June 2010:
https://archive.is/8VFLc

Liz mentions two of his friends (probably troon polycule members) moving into his Somerville house. He also named the house the "
Hive of Scum and Villainy". Liz often used the house to host social events like communal dinners and game parties... Does this sound familiar?
If you've forgotten, check out the post about Liz Fong-Jones' Fetlife activities:
Liz Fong-Jones had a FetLife account ("lizthegrey")
On his Fetlife account, there were several "Tickle Munches", "Rope Events", and even an "Age Play Munch / Game Board Night" being advertised. It's clear now that Liz was hosting these degen events
at his own home, the Hive of Scum and Villainy.
From the blogpost excerpt above:
and even packing 90+ people in the house for an unconference earlier this summer
An "unconference" is apparently a
hypnokink thing. It was mentioned on Liz's Fetlife account as well.
Pretty interesting then that Liz Fong-Jones allegedly convinced a troubled 17 or 18 year old to run away from home and come live at Liz's house - the same house where Liz's polycule lived and where a bunch of Fetlife events were being hosted.
