If one person's ass is penetrated by two objects, it is generically called double anal penetration (sometimes abbreviated dp).
Double-Double: Multiple penetration by four penises. Two penises in the mouth and anus simultaneously.
Triple-Double: Multiple penetration by six penises. Two penises in the mouth, vagina, and anus simultaneously.
Mark and John will D.A.P. her ass!
Mark and John will D.A.P. his ass!