Tess - i thin that there a several issues to resolve (obviously) here, but tow that stand out are
- the assumption that because you're at home, you have responsibility for everything there. it's a common situation, and one that feminists have battled for decades, but perhaps you should just 'opt out' for a night like your dh did, to make him see that you are being taken for granted here, and expected just to pick up the pieces of everyone else's problems.
- the idea that dsd is still a child. well, yes, she is, BUT she is a child who has had sex. imo, if someone has sex, they should be prepared to be a parent. if they truly are unable to deal with that, they shouldn't have sex. there's no point in preaching to dsd, but she HAS had an adult relationship, and is facing an adult problem. to resolve it, she needs to become more mature. of course, she won't manage overnight, but just taking the problem away from her by caring for the baby, won't make her grow up & will lead to endless further problems. i think you need to get your dh to see (perhaps not immediately) that just solving the problem for her is NOT in her best long-term interests. if she wants to have a child who loves her, then she needs to care for that child, not you.
i don't know how many anecdotes you need, but dh is the child of a teenage mum (though his mum was 19) who ran crying back to her parents. dh's gran pretty much raised him for the first 5 years (his mum was in the same house, but went out to work & slept through the nights). dh spent his entire childhood missing his gran (his mum & he moved away when he was 5), his mum never acted as though she actually enjoyed dh's company, or showed him much love, and dh says he would be happier if he never sees her again. still loves his granny though. as you can imagine, there's been a lifetime of pain between him & his mum, and still no resolution now - he's 43!
i think you are right to be concerned that if you just go along with dsd having the baby, you become the main carer, etc, then that baby will see you as the parent, not dsd.
your dh must be feeling awful atm, though. it sounds like he just wants to 'rescue' his little girl & let her still be a child. it's a very understandable reaction. it also sounds like he wants someone to blame. in the absence of not knowing who the father is, you become the next target (along with himself) as he can't bring himself to blame his dd.
feel so sorry for you, and there are no easy practical solutions.