Front wall corner positioning usually leaves room modes unchallenged. Four subs will reduce, if not eliminate the rooms modes altogether as well as the timing issues. Requiring less gain from each sub and creating a wonderfully tight room lock.
Personally, I’d map the rooms bass modes by using one sub at the listening position playing test tones and preforming the crawl test. Relocating your current subs near those modes and daisy chaining them wirelessly or using inexpensive custom length RCA interconnects from Blue Jeans cable.
Properly positioned, two subs should load the room more efficiently and reduce bass modes. Adding DSPeaker or a third DSP equipped sub with greater low frequency response would become the master to slave your current subs to produce the character your looking for from your subwoofers. They need not match.