Aw unfortunately I guess parameter 8 can't be just 2 either as in previous scripts(which had team of 3) this parameter takes even different values. This must be defined somewhere in the script and parameter calls exact menu. Like parameter 0 = all characters available, and next parameters must be defined in the script to set which characters were already choosen to not show them. I'm trying to check line by line how that field works now, couse guessing just leave more questions.
It's damn long and have hell lots of if's, and my guess adding a choice of 3 will be equal to even more if's... >.>
Edit;
Oh well hopefully I was wrong, I just tested the game by setting this very same parameter in script 5 in HEN group to 0 and got "select party of 3" ;p but even if it works soo easy it still bugs me, what exactly values of this parameter does, couse there are more than just 0 and 8 used there. for example 4, 5, 6, 7, heheh but I'm too lazy to try them all now, maybe I link field from last save directly to seph scene to test it later, running it all X times is just too slow.
I noticed that with 0 it wasn't just make party of 3 but also flashed with press start or something(lol short memory syndrome), probably one of those other parameters would be better here. And also what bugs me, what would happen if you would set it for a party of 3, or even without setting it a party of 3, just with Aerith added IF you wouldn't have Vincent and Yuffie, my guess it wouldn't turn the menu to set third party at all as those checks before test if you have them and if you lack just one then third party is most likely automatically set with last character too.
In other words even if setthing this to 0 works just fine, there would need to be another if's to remake in case player wouldn't have Yuffie or/and Vincent. <- through that's not too important as if somebody want Aerith back surely have all others too:P.
Edit 2:
Now I dunno anything. I tried setting this parameter as 5/6/7 and game allowed only 1 party lol, I dunno then how those parameters are used in scripts around that, nor why changing 8 to 0 changed only this script(not sure as I didn't added Aerith to this scene and soo I couldn't accept 3 squad having not enough characters), while changing to other values stopped scripts for second and third party to work at all;O. Or maybe they use something from previous scenes? As I linked las4_1(where I had last save) to lastmap to test those changes faster. Had enough of it for one day.>.>