Must one re-perform ghusl if, while praying, he remembers that he had another wet dream during a second sleep, especially if he suffers from waswasah and cannot differentiate between discharges that necessitate ghusl and those that do not?

One ghusl (ritual bath) is sufficient for two instances of nocturnal emission. Similarly, if one becomes impure multiple times due to intercourse with one woman, or several women, or nocturnal emission, or a combination thereof, one ghusl is sufficient by consensus. Therefore, you are not required to repeat the ghusl, and your prayers are valid.