If it were me doing it (you're describing a major component of my primary day job here), I would extract and reverse-engineer all four installs, and create from scratch a single unified install that did the entire thing from one clean setup program.

If you are not good at that sort of thing, it gets more tricky. Rob's suggestion of a round-robin control program could work, but only if the installs in question don't need to do reboots as part of their installations.

Note that just because the installs don't reboot your one particular test machine, that doesn't mean they might not reboot someone else's machine. The reboot thing might be needed on some system configurations and not on others.