I would start by level matching all the subs to around 72-73 db at the primary LP. Do this one sub at a time and check to see that the combined spl is going up 1.5 to 3 db to rule out cancellation. Then run room correction. This is very doable but, may take a little time. This is the procedure that I have used integrating 3 non-identical subs. Because you will be using 4 subs, you may gain significant headroom in the system and over driving a sub will not be as major of a concern.
Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus 200 Five, Dayton 18 Ultimxa Dual Sub Cab(2), Dayton 18 Ultimax Large Vented Sub Cab (2), on Berhinger I Nuke DPS amps, Samsung BDP F 7500, Asus/My Book Live HPC 4 TB
Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500