I disagree about ignoring. Support is important. Where you draw that from is your choice. Choose wisely.
My take from the information provided. Your FIL is giving common, yet bad, advice. Given the disparity in the responses from each of you IL's it does make me curious if there was infidelity. Could just be a difference of opinion - lord knows there is plenty of that on this topic.
In the end you get to make the call, however listening to people who have cared about you and you have been able to depend on it just wise. Your gut is normally pretty good also.