Washing Paint off Figures

Heyo, im a newbie painter and I attempted to paint some of my spartans. Needless to say I goofed a bit 🤣 I would like to restart and clear off the mess i made.

My question is 1) are the halo flashpoint figures plastic? Im 99.9% they are. Just wanted to confirm before putting them in anything.

2) anyone have recommendations for cleaning off these spartans?