The basic plot has been done and given the ok a while ago. Probably even before the sale of LFL was made public.
How many drafts it takes to get an actual shooting script from that same story is a good question though.
In the interim the big three could be written out if they refuse to come on board or are difficult in negotiations.
They appear to not be important to the plot and are just window dressing.
The story obviously will be centered around the younger actors who will be playing their kids. Whether they are young adults like in their 20's or teenagers has not yet been said. Nor who will play them or even their names.
They tried the prequels with a new young cast and that worked extremely well, lol.