I'm a bit slow/dense, but you seem to be talking about two separate trees:
One with two trunks and
another that has only one.
Regarding
the 2-trunker:
My basic approach would be to make one trunk shorter than the other. That means cutting the top off one, so I would choose the one with an uglier top and would prune it just above a branch. That branch will, of course, become the top/apex of that trunk. While the initial chop/cut would be flat across the stem, the stub will eventually die back to a slanting line that you will later trim to match. This will take a long long time to bark over, so you would prefer that this scar will be out of sight (to the back as you will most often look at it. There is always the possibility that it doesn't work out as planned. Your only option will then be to hide it with foliage. All you can do is to think this thru before you cut, hope for the best and deal with what actually happens. I cannot see enough of this tree in the pic to be more specific. But no matter, you need to decide.
Regarding
the single trunker:
I think all that needs to be done is to reduce the foliage load on top to match what you've got on all the other branches. Maintain this balance every year (in late summer or fall) is about all you've got to do = remove old needles. Over time things will need to be cut back or else your tree will just get bigger.
You can decandle, like with bonsai (even though it might turn into a big job after a while), if you want shorter internodes and/or shorter needles and to stimulate some additional back budding. In your area, the rule of thumb is to do this about 100 days before first frost (which appears to be about 7 Nov) or about the end of July in your location. Doing it earlier, say in early July, will not shorten the needles as much (in other words you can adjust needle size by varying the date you candle prune). Pretty much regardless of timing, the internode lengths are reduced considerably by candle pruning.
