Hello Stewart,

If you're looking to harvest crabapples, then I recommend getting a different variety of crabapple tree or even an apple tree that blooms at the same time your chestnut crabapple trees bloom for a good harvest. Family relationships in apple trees discourage cross-pollination and I'd hazard a guess that may also be true when growing crabapples for harvest.

If you're not interested in harvesting crabapples from the trees then it really doesn't matter what tree pollinates them.

Good-luck!