If there are no leaves on the one crabapple by this tim, it is probably dead. As for what happened, it would only be a guess: something with the site, soil, drainage, damage to the bark, disease - many possibilities. As for the one that had a few flowers, there could've been frost damage to the buds or possibly poor conditions when the flower buds were set in the fall. Have you pruned the tree? It helps to open up the canopy and remove all the watersprouts that crabapples develop, and which are non-flowering branches. If the tree is healthy otherwise, with abundant foliage, I wouldn't be too concerned. As for the birches, similar situation - if there are only a few leaves at the top, it could be that the tree has declined to the point of no return. The best thing to do is to keep the tree healthy by minimizing stress around the root zone, watering during periods of drought, and fertilizing to encourage vigor. You might consider having an arborist look at them to give an opinion as to longevity and/or necessary pruning to keep the tree healthy.