How many...

[idgy]

inverts can you have in a 58 gallon tank?
Also, I have two different kind of polyps in my tank. When they expand will they sense the other and not expand into the area of the other one?

 

[wax32]

If by inverts you mean crabs/snails it would depend on how much algae you are growing. The often quoted rule of 1 per gallon is way too many IMO.
Sometimes corals will grow over each other with no ill effects but sometimes one will kill the other. What kind of polyps are we talking about?