Good news as far as the insects go. Both are beneficial non-stinging wasps which parasitize other insects. The narrow insect with the long tail -- it's actually, an ovipositor -- which is used to lay eggs in the insects that made those holes in your tree. The other insect which resembles a fly is likely doing the similar thing, but it may be going into the holes to locate the borers.

But the news about your tree is uncertain. Harlequin trees are marginally hardy in our region. Most likely the portion with the holes died some years ago, and then the borers moved in.

To obtain a first-hand opinion about your tree, I suggest you contact several Certified Arborists for an on-site evaluation; they should be certified to evaluate potentially hazardous trees.  Compare their opinions about whether the tree is stable enough to remain or if it should be removed, and then decide how you will proceed. You can locate Certified Arborists in our area if you search with zip code at  Trees Are Good at http://www.treesaregood.org/findanarborist/arboristsearch.aspx.