Mickeymom, I would wait to add the tickets until you find out exactly what's on them. If enough years have passed the child ticket will need to be upgraded to an adult ticket anyway. For tickets that have never been used, they can be reassigned to someone else in
MDE.
I added an old no-expire ticket from 2007 to MDE for an April 2013 trip, I probably did it in Feb. 2013 to book FP+. I thought my ticket had 1 park day left and I know it has pluses left, I believe 4 (I usually write on the tickets as used). So the ticket showed up in MDE, but it had no park days left. I rec'd some msg, I don't remember what it was. The pluses (waterpark, DQ, etc) didn't show up at all. I called Member Services for help as I was pretty sure I had a day left but it turned out I didn't. MS didn't want to get into checking the pluses, said I could use the actual ticket at the gate for those, and said I could have ticket checked at Guest Services or hotel concierge. I didn't press it, as normally old tickets were not checked on the phone (I've read some have had success), and the checking process takes a long time, especially if you have 10 or 7 day no-expire tickets. I didn't bother trying to add any other tickets at that time.
I've been on 4 trip since then and haven't had the old tickets checked yet! Mostly because I didn't want to devote the time to doing it. I have 7 tickets for 5 family members. I know there are a couple park days there, but mostly pluses. Going for a nice long vacation this summer and will make the time to get them checked.
If the tickets were part of a package they may be able to tell who the tickets were assigned to. If the tickets were purchased someplace other than as part of a package, there won't be a name associated with them, only possibly a finger scan, and as far as my previous experience tells me, the only way to find out who a ticket belongs to in that case is at the scanner. We have all our tickets signed.
Your last question is a good one. I have no idea. I'll ask this summer. I have a feeling the old tickets would still work for park entrance, especially since I was told to use the one I entered for the pluses.