My sister has been married for several years. As I don't live in the same city as her and her husband, I don't spend much time with them and really don't have much of a rel
ationship with her husband beyond seeing each him at holidays and exchanging occasional e-mails and Facebook posts.
He sent me a message on Facebook recently, saying that he and my sister were going through a rough patch and started telling me about their problems. I don't want to get involved in these problems; I know my mother has, as my BIL has talked to her about them as well, and it's caused some problems in the rel
ationship between my sister and my mother. Luckily for me, my computer was low on battery and I was able to simply say that I couldn't talk as my computer would die shortly.
My two questions are as follows:
1) How can I tell him gently that I don't wish to be involved in their marital disputes? I know I could simply say, "Look, this isn't really any of my business, please don't tell me these things." But that seems a little cold to me. Does anyone have suggestions for wording that conveys the same idea but isn't as abrupt?
2) Should I tell my sister that he's told me these things? If it were me, I would want to know. But as I've found from reading these boards regularly, not everyone would

Do I have an obligation to tell her, or is this a personal judgment call where I weigh the pros and cons of telling her and decide?
Thanks for any help you can provide.