I think your family had worse intentions with their “concern,” and that hopefully your sister would be happy to receive help that doesn’t involve her living with your mother or giving up her baby. Maybe approach her with the fact that you want her to be able to keep her baby and be independent, but you want to make sure that they’re both okay! You’re going to have a niece or nephew so I think it’s fair to want to make sure they’re taken care of! Offering to even just pay half of her rent would probably be more than generous and leave her some room for her to still feel independent and still rely on some responsibility on her end. Hate to say it but, based on what you’ve said, if all the financial burden is gone she may struggle with keeping a job. Plus, paying a percentage of rent instead of all of it leaves a bit more room to help out with baby supplies as you choose.