first V in tree trunk has black mushy hole why?
Although I appreciate you photos, I cannot tell a lot from them. It appears that your tree has some form of heart rot. A fungus has probably gotten in through a wound in the bark over the last few years, and it is decaying the non-living heartwood of the tree. The tree shows little distress because most of the health of the tree depends on the living, outer tissue of the tree.
However, heartwood is necessary for maintaining the structural integrity of the tree. I recommend calling a certified arborist to discuss your options.
The ants you are seeing might be a secondary problem. Carpenter ants are attracted to soft, rotting wood. Here is a link to a University of Minnesota article. Check it out and see if you think you might have carpenter ants.