For me, I could see Chespin being a pure Grass type. However, I hope it turn into a Grass/Fighting or Grass/Dark or even Gass/Steel
Chespin is a combination of chestnut and pin. It may also be from chinkapin, the name of some species of chestnut.
Harimaron is a combination of 蝟 harinezumi (hedgehog), 針 hari (needle), and marron (French for chestnut).
So this what lead me to believe it going be a pure Grass Type since the only have a Chestnut and Pin and it's japan name is hedgehog and needle and marron (French for chestnut)
Froakie may be a combination of frog and croak.
Keromatsu is a combination ケロケロ kerokero (onomatopoeia for a frog's croaking) and 沫 matsu (bubble or foam) or 飛沫 himatsu (spray or splash).
and in French Grenousse fom grenouille and mousse.
So Water and Poison doesn't sound off, but I hoping it's be Water/Flying or just pure Water.
Now for Fennekin
Fennekin is based on a Fennec fox.
Fennekin may be a combination of fennec and kindle.
Fokko may be a combination of fox, 狐 ko (fox), and 子 ko (child).
I believe Fennekin going be a Fire/Ghost or Fire/Psychic because of a Spirit Spirit. I also believe it could be Fire/Rock or Fire/Ground because a Fennec Fox is a Desert Fox
So to me
Fennekin be mostly Fire/Rock Ground Ghost or Psychic. That if it's no pure fire type
Froakie be mostly Water/Poison or pure Water
Then Chespin all I really getting is Pure grass.