Personal opnion
Charizard -Fire/Dragon I think many people would agree to this change
Blastoise - Water/Rock* perhaps water/steel more for the cannons though water rock would be an interesting concept though design wise I don't see it quite there
Sceptile - Grass/Dark* it's mega is part dragon why not make grass drag?
Blaziken - Fire/Flying* I like the original typing but it would make more sense
Swampert - Water/Ground
Serperior - Grass/Dragon* totally agree
Emboar - Fire/Ground* how about fire dark? or fire normal
Samurott - Water/Fighting* water psychic like a magic unicorn lol I'm joking a second element would be nice but fighting feels slightly over used in starters your ideas would change that I know, perhaps instead water rock the armour could be made of coral or rock or water thunder?
Chesnaught - Grass/Steel* sounds viable enough
Incineroar Fire/Dark looks more like a wrestler then a dark type despite it's official typing