Eiffel Tower - how to get tickets to the Top level (sold out online) + policy for wheelchair?

If your mother is in a wheelchair you will be ushered to the front of the line. They will do this in all lines for museums too.. the french are very considerate that way. As long as they see your mother in the wheelchair..

Second level is pretty good by itself, if you can't get tickets to the top.

The official Eiffel Tower website clearly states that wheelchairs are not allowed on the top level, but may go to levels one and two. In addition, I don't think it is possible to buy a ticket from the second level to the top level on the tower any longer. There have been some major changes to the Eiffel Tower access. Long pedestrian detours through a construction zone are part of this. Give yourself a little more time than you might have anticipated to make your way through this to the tower.

The following website has a lot of information that you may find helpful.
https://www.sagetraveling.com/Eiffel-Tower-Accessibility

I'm not sure that all the other adults would enter the same way or just a companion to help her.

Carol is correct that you can no longer purchase tickets to the summit on the second floor. This would need to be done at the ticket counter before you enter which would involve a very long wait, probably at least 2 hours.
The only other way to get summit tickets would be a tour through a third party.
Views with the tickets you already have are amazing.

For our trip last month, we booked Fat Tire Tours' "Champagne River Cruise & Skip the Line Eiffel Tower Ticket" to get us access to the second and third ("summit") floors of the Eiffel Tower. As previously noted and by what we saw and heard, you cannot buy a separate ticket to access the third floor on the day of visit. Fat Tire Tours also has separate "skip the line" tours for the Eiffel Tower.

Skip the Line Eiffel Tower Tour with Summit Access

I was quite satisfied with the 2nd level, as others are saying. Due to my fear of heights I only pre-purchased that level (in 2016), but once I got there and felt comfy about the whole thing and the elevators, I felt I should go to the summit and bought my supplement on level 2, which you can't do anymore. I wouldn't waste valuable time waiting in line below, just go to 2 and enjoy, it's a lovely experience.

I, too, didn't get tickets online in advance (they were sold out). We went in the evening, in June, last summer. The line was relatively short, in my opinion. (My fiance would probably say the line was long, since he had a ring in his pocket, to propose to me.) People who had advanced tickets also had to wait in a line, so depending on what time of day you are going, you could add 30-60 minutes to your visit, but how many times are you going to Paris with your whole family? Wait in the line. Take pictures from the ground, looking up (it's really a neat perspective) while you wait. Get the tickets to the summit, if you always wanted to go to the top. But....

The long line isn't to get in, it's to get from that 2nd level to the top. Figure an hour minimum, but probably 90 minutes plus. When you get to the top, it's crowded. Really crowded. Tripping over people kind of crowded. There is an interior area that compares the tower's height to other buildings around the world, and some windows with not-too interesting displays outside. Champagne at the bar is about 20 euros per glass (but is a nice treat if you just got engaged!). The views are great, but not necessarily any better than on the second level, and there are more heads to look over. Our pictures at the top were mostly of us; the ones on the second level were of the views. If your mother can't go all the way up, she's be content staying on that level.

All of that said, I'd recommend going just before sunset if you can. It's cooler, the sun setting on the horizon is exquisite, and when you come down, you can sit on a bench and enjoy the light show.

FWIW. We had advanced ticket in October a couple of years ago and our day was literally the ONLY day it rained all day that month. We had the tickets; we went. It turned out to be great. The only people there were those with advance tickets so it wasn't crowded. The views were really quite amazing in the rain. It seems like it would be a terrible idea -- but worked out.

https://janettravels.wordpress.com/2016/05/16/the-eiffel-tower-in-the-rain/
So consider a try on a rainy day; you won't want to go up if it is fogged in but the wisps we had were actually quite lovely.