I am kind of confused in here, is sex between Eiza and MC count as penetration?
It does. Though I guess either Carta either forgot that scene, or he's not counting it cause Eiza is a side girl, and not one of the main girls (Luna, Gracie, Isabel, Cordia).
My guess is Eiza won't be the only side girl in the game though.
There's following girls (with potential to become sidegirls in the future I'd imagine):
- Siobhan, the Scorpion princess (became pretty obvious after the stealth mission)
- Amita, one of twin nuns Capos
- Amata, one of the twin nuns Capos
- Leliana, Elite soldato (not much of a presence in the main story yet, more in contracts, but who knows in the future, I hope she becomes a side-girl)
- Caterina, rollerskating Capo (she seems to be lean more towards women, particularly Cordia, but here's hoping she's at least bi-sexual)
Characters from Wilfred's Division such as Elita and Onorina, it's a bit too early to think about whether they can be side-girls or not (even though I did love Elita giving MC hints to give "Serpent" the high-five).