You can scan those LMT etickets into the app right now. The exp date will say on the app they are 2 weeks from now, but each day the exp date is forwarded, so don't worry. It is just a glitch.
You can very simply add maxpass to your tickets once you are actually scanned in the park for that day.
Get there early and while you are standing on Main Street waiting for RD, you can purchase maxpass for your whole party (or just a few people).
That maxpass thread for
Disneyland has some other great tips, but it is getting pretty long, so you may have to sift through it a bit.
https://www.disboards.com/threads/maxpass-digital-fastpass-discussion-thread.3592571