@Foodchain, yeah that's basically what I did. I forced the max party size reached flag to always be cleared during the check. This could probably cause even more issues if you reached act 2 and you recruit mercenaries as well, although at this point I'm not even sure you'd be able to reach act 2 with all companions. There's also a max party member value you can set. It's default 4, I changed it to 6 just in case it looks for it elsewhere.
As for save vs new game, I did load the mod into an existing save of mine immediately on reaching FJ and it worked. I wonder, in your existing save you had already recruited someone and thus the recruitment script had already loaded? Perhaps if you have already recruited someone the new script won't load.
With respect to the "character assign" screen, I'm not entirely sure what this is. I didn't play the EA so I'm not completely familiar with all the DOS2 options. Is this the "party management" option in the escape menu? Is this a coop thing? I've never actually used that option but I do see it only has the first few companions.
@Parkan, I'll see if I can upload to the Nexus but it might take some time. I've never used the Divinity Engine before today so it might take a while to figure out. I just picked it up today since I was also curious about getting 6 party members to work.