A curious question

what are the chances that my mewtwo encounter spawns a raikou?

I think same as any other encounter, raikou and entei have the same chance of spawning every time you get a encounter (not a 100% sure tho)

and now i got a raikou with my meloetta encounter

and now a entei with my hoopa encounter. what are the chances of them spawning lol

Really high. If I were you, I’d get them out of the way before they become a bigger nuisance than they already are.