I plant my tropicals out in the garden... and dig them back up and put back in pots indoors for the winter.
While I don't have Cherimoya, the plants that I put in the ground for a few months do a lot better than the ones that I leave in pots.
Changing the soil may help... especially if you went for a better draining medium.
Kinda surprised that you would attempt growing so many Cherimoya if there is no chance of ever setting them out in a permanent spot.
