The PVC won't explode, but the performance of two pumps dumping into one (possibly already undersized, just based on many sump installations I've seen where pipe size was cheaped out on) pipe the same size will be much lower than individual pipes, or a pipe of increased diameter after the join.
Examine your pump(s) - if there is any reducer on the outflow piping, you might want to start with simply increasing the pipe attached to the maximum diameter that the pump is natively designed to connect. If you propose to join two discharges together, you should be increasing the discharge size to compensate for that (as well as having a check valve on each individual pipe so that one does not pump backwards though the other.)
If joining two 2" pipes, you need a 3" pipe to take the full flow of both (pipe capacity is proportional to the square of the diameter.) Likewise, using a 1.5" pipe when your pump will take a 2" pipe is not 75% capacity, it's 56%