It appears that you have the right aproach by applying fungicides but timing is off by quite a bit.  What you have in the leaf spots is Cedar-Apple Rust.  This is a fungus that is hosted by Cedar trees in your vicinity which is carried during wet weather to your crab apple tree.  The spores will continue to affect the leaves until they eventually fall off during August and September way earlier than they should be falling before winter months set in.  The fungicides should be applied when the flowers begin to develope on the tree in early spring and then again when they in full bloom and then when the leaves are almost fully open.  It seems like a lot of bother but you have to give the tree some tools to help protect it against the fungus.

You didn't supply a picture of the branch so I'm not sure what is going on there.  And you're probably correct about the former wasp nest.  No concern there as the wasps don't have to home to return to.

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