Hi Alice,I'm glad you got the update working and hopefully you won't have any problems with the next update if you repeat the same process.
As far as lore goes, we are working to fill out the wiki https://allele-origin.fandom.com/wiki/Allele_Origin_Wiki:%E2%99%A1 with more content but it might be a slow work in progress. You can also feel free to ask questions either here or in the discord https://discord.gg/4Wj5383U5Y community if you're ever confused or wondering about something.
A lot of my writing can be inferred or speculated upon from gathering information from the library or various optional events so it's very possible to overlook or miss details that won't detract from understanding the main plot but maybe provide some additional insights.
Spoilers to answer your current questions:
The mc ashes are used in a ritual described in the library. Those who receive the blessing become like Isaac, immune from the plague, stops aging and possess higher strength and recovery than a normal person. Those who fail the ritual, become 'others', cursed to a monstrous, feral form. One of Isaac duty as the current heir is to produce another blessed heir to the Ashborne family bloodline, but he lost many children to become others and no longer could handle the emotional distress it caused him. As a last resort, he attempted to break the traditions of his family and resurrect the sacred ashes to free him of his duties. He has a love hate relationship with the MC because every good thing and terrible thing in his life he attributes to result of the ashes, though he recognizes after dinner that the MC has no actual intention of anything Isaac went through so his feelings often conflict. He feels intense dependency on them regardless. As far as his previous relationships go, it's hinted that he must have had several children by many wives in the past (given the shorter lifespan of the infected) though he never speaks of it. To get into spoilers, there were most likely political arrangements that he didn't have much romantic feelings about. He is only ever mentioned to have cared for his children, especially his first daughter. He is indeed, more passive and shy when it comes to showing true affection and intimacy. Hope this helps!
Good luck and best wishes with your thesis!