I really know nothing about it, but I do have a friend who was at the seminary in the 80s and he said that he is sure that Williamson will reunite if the group does. He's a pretty good judge of character and he thinks Williamson's reputation is a little off from how he really is. I have no idea, but this person thinks all four bishops will act in unison, and I think he knows what he is talking about.
FWIW, New Catholic over at Rorate Caeli agrees with your friend.
"I would add the most important information that reports of a division among the four bishops consecrated by Archbishop Marcel Lefebvre and co-consecrated by Bishop Antonio de Castro Mayer in 1988 are wrong -- there is no such division."
I often think all the knocks against Bishop Williamson come from people who would object to and be scandalized by the following statement:
"To train their children in the practice of virtue and to pay particular attention to their domestic concerns should also be especial objects of their attention. The wife should love to remain at home, unless compelled by necessity to go out; and she should never presume to leave home without her husband's consent. Again, and in this the conjugal union chiefly consists, let wives never forget that next to God they are to love their husbands, to esteem them above all others, yielding to them in all things not inconsistent with Christian piety, a willing and ready obedience."
(Roman Catechism, "Duties of a Wife")
The sort of objections you sometimes hear about Williamson - that he panned some pop-culture movie or said women should wear dresses normally, seems right up there with objecting to the Church saying of wives: "she should never presume to leave home without her husband's consent", which I imagine many modern Catholics would.