I agree with most of what HopCar said...except for increasing the size of the thru-hull to almost double its specified 3/4" size. Among other reasons I wouldn't do that is the potential to pull in animal and/or vegetable sea life that would be too large to make it into a 3/4" hole. You'd also have to install reducing adapters on both of the toilets to avoid pulling in more flush water than the
toilet is designed to push out. But even if you only teed or wyed the intake lines to connect to a
single thru-hull, if one toilet goes down, they both would.
So I agree 100% with his final bit of
advice: install another thru-hull for the a/c
pump...or if you're really opposed to putting another hole in the boat, replace one of the toilet with one designed to use onboard pressurized fresh water. Get a quote for a "conversion" from him.