The Tomcat can track 24 targets at once and can engage 6 of the 24 simultaneously if it has 6 AIM-54's available to it (in TWS-A and TWS-M modes, the difference is that in -M (Manual) the RIO designates which targets are to be engaged). Since the F-15 got its APG-70/APG-63V1 radar it can also do multi-target engagement with the AMRAAM (doesn't work with the AIM-7) and I don't know the limits of how many targets it can engage/track. The -16, -18, -22 and -35 I have no idea about but I'm willing to bet they can too. As has been said, however, this capability hasn't been added to the TW games.
EDIT: Apparently the APG-70 can track up to two targets at once for attack in a mode called "Dual Target Track" or DTT and can fire one AMRAAM at each of the two targets. Also has the TWS mode which tracks up to 10 targets. Don't know how many fired missiles that supports, however.
REF: http://www.f-15estrikeeagle.com/navigation..._technology.htm