Where is the PI/corresponding author? They really should be the one handling the issue.
I witnessed a similar situation once in my lab, but in my case the difficult co-authors were all fine with the initial submission and then all of a sudden had concerns once the journal sent it back for minor revisions. There was some drama, and they kept coming up with additional concerns and delaying it for months. We brought on another co-author who was more of an expert than they were in the part of the paper where they had concerns, and he eventually won them over and helped it over the line.
To be fair, there is something to be said for additional perspectives and genuinely trying to make the paper better – sometimes you have to humble yourself, acknowledge that you really can make it better, and accept the criticisms even though they can sting.
Ours was an absolutely horrible experience, and there wasn't an easy answer to a mostly political problem. I obviously can't say what's really going on in your situation, but your PI really should be taking the lead on handling it.