Nanskisses anyone reading your last post would be full of sympathy for all the ills physical and mental that face you. But I think most would also say that you and your daughter are tied together in a relationship that is mutually destructive and that desperately needs sorting out.
There is something called 'tough' love. This is loving your child, but realising that the best way you can show that love is by putting space between the two of you.
Princess Diana famously said that there were three people in her marriage to Prince Charles, the third being his mistress. Your daughter is also in a marriage with three people in it. The third person in her marriage is you. And while her husband sounds a nasty and dangerous man, who financially abuses you, he must be constantly exasperated by the way you seem to want to be involved in every aspect of their marriage.
The best thing you can do for all of you is step back. Do not phone your daughter, let her phone you. Refuse to give them or buy anything for them. It would be quite reasonable to say that you have spent all the money you have on them and have none left.
You ask why they treat you so badly when you have done so much. To be brutal it is because you have acted like a doormat that they can wipe their feet on, every demand they make on you you meet, 'loans', expensive presents, you are constantly trying to buy their love and they know whatever they ask you will do. No-one, least of all a man like your SiL, has any respect for someone who acts like that and he will play you like a fish on a hook for his maximum pleasure and your maximum pain..
Your best way forward is to step back. Let them make the approaches, you can be willing to see them, but give them nothing, not even when they act 'bad cop' and then cut themselves off from you, at least for a while. In the meanwhile try and seek therapy that will help you change the way you think and respond to them to a more healthy basis. Something like CBT (cognitive behaviour therapy) This concentrates not in examining your entrails to find out why, just concentrates on making sure you act differently in the future.
If you do this, one of two things will happen either your daughter's family will try and pull together and get their relationship on a better basis and your joint relationship will improve as a result or the whole house of cards will fall down and your daughters marriage will breakup and she and her children will move in with you.
But this will place more pressure n you because you make clear that your daughter ricochets from one bad situation to another causing chaos and upset where ever she goes. How will you cope when she is living with you again.
This is why I recommend CBT. It is functional and just teaches you techniques and redirects your responses to changing how you behave in the challenging situations that face you.
And if your daughter takes her children to visit her father again, report her (anonymously) to Social Services or the NSPCC, there is absolutely no way those children should be anywhere near a known child sex offender. Those children are just that children. You know what sexual abuse has done to your daughter. Do you want the same thing done to your grandchildren? If he misbehaves with them and is in court and it comes out that you knew he was seeing them but did nothing to protect them. Your chances of ever seeing them again are minimal.
There is nobody on this thread who does not feel for your predicament, but only you can get yourself out if it and that requires you gritting your teeth and giving your daughter some tough love.
