Jasper - I like it and its on my list, but I dont think I would actually use it, I find it a tad fem and I'd prefer a more serious name, LOVE it on other ppls kids though. Jasper Morgan sounds amazing too.
Isaiah - Not into it at all. It's a very biblical name.
Josiah - Also not into it. I like Jonah and Joseph though. LOVE Joseph actually.
Noah - WAY TOO common. I know about 6 little Noahs. I'd want to avoid the trend and give him a more original name. You could use it in the middle if you really love it?
Alexander "Xander" - Alexander Morgan sounds really good, but slightly familiar, I'd google it just to check it wasnt someone famous! Alex and Zander and both cute nickname and overall its a very classy choice.
James - Cute but too overused in my opinion. There are lots of names that are just as nice but way less common.
Nathan - I love it! Not sure it goes with Morgan. Nathan Alexander sounds nice. Sounds nice with your other kids names. I really love Nathaniel (thats what im naming my bub to be, I already have a Rory too). Nathaniel Morgan sounds good too.