I have settled on the below, seems to tick all boxes for me. No spare wheels or parts other than the odd tyre swap for the boggy months.
– 170mm 29er Ali FS, the big bouncy enduro
– 120mm 29er Ti HT, the light XC duties with some trails
– 160mm mullet Ali E-bike, Eebs 4 life
– Ali road bike, turbo and fair weather road duties
tried to keep the same parts/brands across the MTB’s which helps for robbing bits when stocks are low