Hmm, I don't really know either.
. They sure have had a cut in day time sleep over the past few weeks, so it would be hard to think that they are still UT, but it is a possibility. I think what they're doing right now is a pretty average routine for 10mo, but it can really vary depending on the LO.
The way you describe the NW sounds like it is still either developmental or UT to me (could be discomfort, but that's hard to say if he's not struggling during the day; although, I'm sure if Everett's getting a tooth through, Elijah probably won't be too far behind). He sure is doing lots of developmental stuff, so I guess we'll go with that and keep working through it. I would try really hard not to intervene though if he's not crying for you. I know you don't want Everett to wake and I don't either, but sometimes our intervention in getting things done quicker ends up biting us in the bum later, because they become dependent on it. My DS woke often at night at this age, and all it took was for me to go in, lie him down, and say my sleepy phrase and he'd be back asleep. But, he didn't stop waking. So, finally I made him lie down on his own for a few nights and he finally stopped waking. Turns out my little cuddle and put down had become a sort of prop.