SIL1 has a lot of emotional and personality problems.
Are you married now?
"one of the dysfunctional habits he has with his sister is to tell her things that he shouldn't be sharing (and are often untrue)"
I would say the "often untrue" part would be a huge problem for me.
Yes, we have been married for 3 years.
Sorry, I'm not sure I made myself clear.
To answer your questions - NO, I do not think you should have this niece to stay at your home.
This is a very tricky one. I have my own fair share of experience in having completely cut ties with one part of the family (an abusive alcoholic father) and having to maintain some relationships that are linked to that person. Firstly, I think you need to talk to your DH very openly and honestly about this, particularly about how you feel about this. Make it clear that you are not judging him, or his FOO or his relationships with them BUT also make it clear that there are some things that you will NOT put up with. Get those boundaries clear, and get yourselves on the same page. You may need the help of a counsellor (a disinterested third party) to help you sort this out.
When you've done that, then you can both work out any ground rules for contact with everyone, and STICK to them.
"My definition of housework is to sweep the room with a glance"
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