Well, you can only use one "The One Ring." And you can only use it on your desired Ring-bearer (unless it changes hands to Sam because of his game text).
However, you can use ARB's as normal companions, for example, just not bearing the ring. Then you have to pay their twilight costs and other such things. Except for Frodo - he's not an ARB (just a Ring-bearer) so you can't use him other than as the Ring-bearer. And there's no way to "give" the ring to an ARB you're using as a regular comp, either.