call a "real" arborist, not just a tree cutter,I can see no reason to remove any tree unless it is in danger of falling down on your house or poses danger to persons walking underneath it. Also call a "real" exterminator to see if you actually have a termite problem.There are many things a home owner,DYI, can do, but I believe these are 2 areas best left to experts
I would definitely rule out a disease, fungus or insect population that is not supposed to be there as it could spread. Where I am both twin cities have great arborists that have all kinds of counsel and advice available. The last thing they want to do is take out a tree but this is an urban forest environment. Try your nearest university also. Your state forestry folks could also be surprisingly helpful in at least figuring out what is going on.