Is it legal to pay two providers to have lesbian sex for me to watch?

No !   But.....Go for it and let us know how it went !  Odds of getting caught-minimal !

and see if there is any specific reference to having to have contact between your junk (genitalia is the legal term) and the person being paid.   Just exposing yourself is enough to break the law in most places, so if your idea is to whack off while the gals play, that will probably be a no-no.   Some state's have laws written so broadly, that looking at underwear ads in a Sears catalog will be enough to get you shipped off to the pokey.

I'm in IL. No, I will keep the mouse in the house at all times during the spectacle.