What to do about manic depressive father in law?

If your father law has a mental illness, whether bi-polar or OCD, he should be receiving treatment and counselling. It seems that you're in a very difficult position as he's locked himself in his home. For his own health and safety, you should make an appointment to see his doctor so that he/she can be made aware of what's happening. I think a personal visit to the doctor would be much better than a mere telephone call, and it would be best if it was actually one of his children that approached the doctor, if that's possible. (Next of kin). I hope all goes well.