Theophilus

Leaving one church and going to another is not a magor issue. It doesn't require a declaration, or balance statement, justification or excuses. I can see were having family gathered under one roof could get awkward at times. The father inlaw migh feel more at ease with a little distance. You might want to discus it with him and get his feelings.
I can't say as I have any experience with your situation.
As close as I can relate to it is that in relationship to my brothers in Christ. I have two brothers ,one a pastor, that I am real close with. We met in a small congregation that literally self destructed about six years ago. We all three went differant directions but kept in touch over the years. One thing we discovered is that when we get together we have a lot more to talk about. Our get togethers are much more fruitful when we bring in input from our separate experiences. It's varied rather than rehashing over stuff we already know about. It could make your relationship with the father inlaw better.
Just something to think about.