Just so you know, catnip "can" loosen inhibitions of all kinds,
including aggressive impulses. In other words, don't be surprised if
the rolling and rubbing devolves into some hitting and bonking. It can.
Also, although there are exceptions, kittens aren't always susceptible
to catnip, so they may get a little freaked by the older cats seemingly
going insane right in front of their eyes. It may work out fine, just
keep an eye on everyone while you do it!