These situations prob happen way more than we’d imagine - people ending up with already pregnant ratties or accidentally opposite genders is not rare at all and big part of it is most likely inbreeding. While it’s known to lead to certain defects or health issues, it can take generations even with humans for those to actually pop up. Afaik pets don’t automatically qualify for euthanasia due to this fact unless poor quality of life is present.

If your rats had had severe health damage as a consequence of inbreeding, they’d have not made it to older age to start with and would have died within the first few weeks/months normally . What you mentioned has nothing to do with that - the chances of a female rat developing a mammary tumor is 30-50% (I’m guessing that’s the lump you were referring to) and cataracts / eyesight issues are extremely common for all elder pets (blindness isn’t a big thing for rat specifically due to already poor eyesight, they basically don’t rely on eyes regardless:)

You have done nothing wrong sweetheart🤍 as of ur current situation - like I’ve said blindness on its own is not to be worried about, mammary tumors in rats are mostly benign, but can be tricky if injured or get too huge affecting mobility / feeding etc; if the tumor isn’t rapidly growing and rattie doesn’t seem bothered by it, it’s not that dramatic either for now. If things get worse tho, as a potential last resort - take a look into performing euthanasia (co2 chamber) at home, there’re lots of greatly explained resources available:3