I have 4 in-laws.
The set that lives close by is DH's Bio-dad and Step-Mom. These are the people who raised him and the ones he refers to as Mom and Dad. In fact, he gets offended if someone refers his Mom as his step-mom. Technically she is, but the woman raised him as her own from the age of 3 and she is a lovely woman. I get along GREAT with these two! At times i think i tolerate them better than my own parents. My MIL is a wonderful, sweet woman. They treat me like a daughter. FIL is also a great guy. Super sweet, understanding, and just a fun person to be around.
The other set is different issue. Bio- Mom and step dad. This MIL abandoned DH at the age of 2, never raised him. We see her once or twice a year. DH is semi-estranged from her and their relationship is fragile. She HATES MY GUTS. She tried on several occassions to break us up, and tried to stop our wedding. I play nice with her and basically follow DH's lead. We keep a distance, minimal contact, and don't allow her to close into our lives. She has never been inside our homeas we always meet at outside locations. Yeah... it's tense with her to say the least.
Her husband however is an alright guy, no complaints about him. We have not seen him in 7 yrs. He has no interest in us, but that is perfectly fine. MIL always travels without him.