The lyrics to an old blues song come to mind.
"I'm three times seven
Lord that makes twenty one,
ain't nobody's business what I do."
If you want your daughter to move out of your place and maybe go somewhere that won't be as safe as your house then, by all means, try to dictate things like religious/sexual preference. I say this because, having grown up in an abusive situation, it is what she's used to and, believe me, she'll have no problem finding her way into a new abusive situation. It also sounds kind of manpulative to tell her that you'll withold Christmas presents if she doesn't believe in God. Wait, did I say kind of manipulative? Dude, that is TOTALLY manipulative!
That being said, as she is twenty one she is responsible for explaining her choices to others. So if she is a lesbian let her explain that to your parents, if that is necessary. You don't have to let her be abused, just let her defend herself and her choices. Not that being a lesbian is a choice unless, of course, it is being spoken as part of a rebellion.
As you are afflicted by MS and since stress exacerbates your MS my choice, were I in your shoes, would be to reduce the amount of stress I bring into my life. It doesn't sound as though you had a whole lot to say about the upbringing of your daughter so you do NOT have to defend the person that she has become. If anybody attempts to guilt you into taking a hand in something that is basically none of your business, that being the person that your daughter IS, you could tell them that she's had it rough and your main concern is showing her that she's loved and valued and that's why she came to live with you. As far as changing who she is or making her believe in God, not your job. Plus, the absolute best you can hope to do is to get her to make a coerced statement to the effect of "Yeah, yeah, OK, I believe in God, alright?" but you can't make anybody believe. Who knows, she lived in an abusive situation for almost all her life. What if she prayed to God every single day to please get her out of this and in spite of her repeated pleading God never rescued her. Maybe that was sufficient to cause her to not believe. So show your daughter and your granddaughter that you love them UNCONDITIONALLY! Unconditionally means that you love her even though she has her own beliefs and with no regard for what any outsider's opinion might be.
If the people who are so intent on making you alienate her can't hear any of that there's always the Gospel of Go F**k Yourself.
P. S.: The other option, if all of this is causing too much stress, is to kick her and the kid out.
