I have to agree with the above comment about seeking some mental health help and advice. That sounds like a very drastic change in his affect and needs to be addressed.
However you’re also wise to question if possibly, it’s been there maybe under the surface all along and maybe now that he doesn’t have to temper it due to not being home it’s come to the surface?
Gosh I hope he doesn’t have these outbursts when Franks family is there.
Hugs I’m so sorry you’re all dealing with this and I hope you can get some answers.