My fh family is boycotting our wedding

Unfortunately, all you can do is be supportive to your fiance through the situation. Its really his decision on how to handle them, and if he is fine moving forward without them present, then that's his choice. My first husband's sister didn't come to our wedding because she thought I was mean to her (all in her head), and we were both fine with that in the end, because we were happy with our decision.

How does he react to them treating you poorly? I had an ex who stood up for me when his family referred to my son as baggage, but it was a contributing factor in why I ended things, because I did not want to be a part of a family that could refer to a child that way (they also said things like this in front of my son).

I think if anything you need to have a convo with your FH, and it's something he has to handle with them. If he wants to move forward without them, that is his call, just be supportive either way.