How edible/palatable are crabapples?

Some crabs are better tasting than others. Ornamental crabs, to my knowledge none are inedible, but tend to be very small, and high skin/seed to flesh so tend to be too much trouble to bother with. Larger crabs though can be very desirable for some applications. They are often blended in mixed ciders, both sweet and fermented. They will be tart to very tart and even bitter, but when blended with other juices add what many people consider a very refreshing bite to the juice. Candied crabs and apple butter are commonly made with them and they can be used for jams other applications especially mixed with other apples to increase tartness.

There are a wide variations of varieties, just as with full size apples, and some will seem better than other. If they are wild seedling trees rather than grafter varieties, the quality of the fruit may be hit and miss, and even some of the cultivated named varieties may be astringent, especially some which are marketed for their hard cider characteristics where the astringency is desirable. If the particular ones you have will work will be mostly dependent on your tastes and the variety, and how willing you are to work with the smaller fruit. Even the sweetest crabs are likely to have a lot more tartness than a granny smith.

Yes, they are edible and they have historically been eaten although not widely adored as "good eating".

Description: The fruits of crabapple trees are round and fleshy and typically red, yellow, orange, or green in color. These fruits belong to the pome variety and attract mammals. They tend to be beetween [sic] 1/4 and 3/4 inches in diameter and mature in dense, showy clusters appearing the months of September or October until December...

Because of their sour taste, crabapples are usually not eaten raw by humans; they are sometimes used as condiments Often used for cooking flames for smoked foods, crabapple wood releases a pleasant aroma while burning very slowly.

Quotes from YaleNaturewalk.edu