I had typed up a long response, only to have my computer suddenly shut down and lose it all. Ugh. So, I am going to try to redo it in a short version.
1 - Child is nearly an adult, not a youngster, but doesn't yet drive. (This may be the proof to the kid, finally, that life can be easier if they will learn to drive.) Our kids have to learn to navigate this stuff on their own now, including telling dear old dad who they will and won't ride with that he proposes to drive them, regardless of the event involved.
2 - Pictures and wedding are two separate events (I assume a pro is doing the wedding ones), and pictures aren't "engagement" ones, as those should have been done last year. Thus, these are not time or event sensitive.
3 - I have no info on the wedding past that which xwh has shared with the kids that has gotten to me; they don't even remember which day of the weekend it is and don't know the venue location. Further, it seems xwh has not mentioned a rehearsal to them, though they should be at it, and time is running short. (Not my responsibility to remind xwh he needs to communicate such to the kids either.)
4 - Mow tried using a false accusation of stalking as a way to get me arrested and went to the extent of fabricating "evidence" in the form of a large document, meaning was willing to put a lot of time and effort into said attempt. Thankfully, it failed. I wouldn't put it past her to try again. Were I to go near the event that day, though I remain in my car, should anything go "wrong" with the event, I would fully expect to be blamed....
I was not able to view your advice prior to the child bringing up the issue again - this time mentioning feeling "funny" (as in, it being awkward) having me drive for the pictures. I was then able to be open and honest with the child about not feeling comfortable having anything to do with xwh and mow "coupling". I further added that the same went for the wedding, noting it is xwh's wedding AND his weekend (parenting time), and, thus, his responsibility to see to it his kids have a way to get there and back, if he wants them able to attend. I said if there was an actual emergency situation, I would be there for the kids, but regular old transportation arrangements in this case are for xwh to handle. The child seemed to understand and even agree.
Honestly, I think xwh has simply forgotten he needs to arrange transportation for the kids, as he always has relied upon me to be available and willing to handle that in the past; for this event, though, I think it is a bit outrageous to assume that. Besides, as I would not be attending this even if invited, it has always been his responsibility to make the arrangements and not mine. (Similarly, when I took the kids on vacation together and they were starting/ending the trip in different locations, it was my responsibility to arrange things, not xwh's.) As to mow, she likely has deliberately ignored this item, as the drama of xwh's kids maybe not being able to attend the wedding plays into her MO of playing the damsel in distress to his KISA and her vilifying me perfectly, never mind it is unnecessary. (Plus, then she can match up with the drama around her ex's wedding where her kids were not able to be a part of things, also likely due to mow's choices, but for which she vilified her ex.)
Will all this create a problem for the pictures to be done, at least for now? Maybe, but I fail to see this as my problem. Is it a complication for xwh for the wedding? Yes, but that one is definitely not my problem - that was always going to be a complication for him for the wedding, and it is his fault entirely he has forgotten. (Perhaps now youngest has pointed out the problem to xwh so he can address it; maybe I just saved the day, in truth....not that I expect xwh/mow to view it that way.)
As an aside, I am surprised the event is even being held, given the virus situation as cases are high where we are. I am also surprised youngest, who has been anxious about the virus, is still planning to go, given it does not appear to be a small, intimate event....which brings me back to not understanding how this is even being held at present time. I can only pray there is enough distancing that my kids do not get sick, even if someone with the virus is present.
So, I did not see your advice first and did the exact opposite of what most of you stated. I don't know if that means I blew it, or maybe, for us, this is exactly what needed to be done. Time will tell. I do appreciate all who responded, though!