If three people own it, then all of them are responsible for the upkeep. If the others are not present (live too far away etc), then perhaps you could divy up the most pressing work. Maybe the others can contribute money while your contribution is the work and information gathering. You should agree on this in writing in case you'd later have disagreements and they claim you did not pay your share of upkeep or anything. Some contract that all three contribute, 2 will contribute x amount of money and you will contribute x amount of hours in lieu.
What you need first is information: any old contracts or information about the building that you might have, year of building, which materials were used, type of insulation, type of heating (is there none so far?).
Armed with this kind of information, you can see if there is information from your city administration or citizens advice or similar about where to start when you want to renovate a building or insulate it better. There were a lot of campaigns about energy efficient buildings, so there must be some points of information.
YT is a rich source for DIY building and renovation, but check the credibility of people first, not every YT builder actually knows their stuff and some "solutions" can be quick fixes with long-term problems trailing about. Others are just ads for equipment companies, so look around first before you act on anyone's advice.
There were youtubers who built their houses from scratch, there are also many DIY renovation channels by women, from people who started out knowing not a lot or coming from totally different professions but taught themselves.
The keywords you gathered from knowing what type of house you actually have and its specifics, combined with information by foundations, administration etc will help you find the right videos.
But at the end, if you really do not want this house, then ask if the others would buy you out.
The most important aspect would be to stop mould, and since it's summer, maybe you can do a few things now that are easier in good weather.
I also read of schemes where you get renters that will do renovations in exchange for a reduced rent. But even then you need to know the basics of what is going on and agree on a plan with them, not just let stuff happen, and you'd probably need to supply the material for them. Also in this case, put everything in writing and into a contract and specify.