You can graft apples of your choice on the apple tree. Your rootstock will have no dwarfing ability so expect a large tree. I would remove all suckers from your crabapples if you want to continue growing in the standard shape of your current trees. They will grow back and need removing again and again. Al

Thanks for your input! what do you think would happen if I cut off the top of the apple tree? Any chance I can make it shorter?

If you cut off the top of the apple tree it will sucker like crazy. You can keep it lower by pruning and training the branches to spread horizontally along with continual and regular pruning.

If you really want some useful advice try to post a photo or few.

Here's a pic of the apple tree.

This is a close up of the first set of branches on the apple.

And this is the crab with all its suckers.

based on your input here, I've decided to prune all the suckers on the crabapple and to remove the apple tree. as much as I hate to kill a mature tree, it is growing right in the middle of where I want my vegetable garden to go.

The trouble with the crabapple pruning plan is that there is a mourning dove sitting on a nest in one of the sucker branches. So I will wait until she's done with her nest. Probably autumn.