Haha well I was trying to avoid the politics... honestly...
As I say, a generalisation - it's sometimes difficult to model intrinsic cultural divides within the realm of EU2's often large & clunky provinces.
Nonetheless, Brabant shouldn't really be able to incorporate the Netherlands & parts of northern France without any cultural penalties, which presumably it would if it had the correct cultures.
Cores are a different matter of course, and I doubt Brabant receives any by event; speaking of which, check Brabant's event file for add/remove culture commands.
You can always suggest amendments if you wish.
I would suggest this, covers most points
1419 GC scenario and Brabant gets only dutch culture
then if human played, they choose option B below
#(1430) The Succession in Brabant
#modified by Jester to nullify RevoltRisk generated by HAU_182002
event = {
id = 3775
trigger = {
exists = BUR
}
random = no
country = HAU
name = "EVENTNAME3775" #The Succession in Brabant
desc = "EVENTHIST3775"
#-#The Duchy of Brabant had been under Burgundian influence for a while already in the decades leading up to 1430 with side branches of the Burgundian dynasty occupying the title of Duke but on the 1st of August, 1430 it formally passed to the control of Philip the Good of Burgundy further strengthening the Burgundian hold on the Netherlands and continuing Philip's moves towards unification of the Netherlands.
date = { day = 3 month = august year = 1430 }
action_a = {
name = "ACTIONNAME3775A" #Let us be a part of Great Burgundy (End Game)
command = { type = trigger which = 3776 } #BUR: The Succession in Brabant
}
action_b = {
name = "ACTIONNAME3775B" #Let us elect a local Count as Duke
command = { type = trigger which = 3778 } #BUR: The Succession in Brabant
command = { type = stability value = -3 }
command = { type = revolt which = -1 }
command = { type = add_countryculture which = french }
command = { type = province_revoltrisk which = 379 value = -8 } #Artois
}
}