How to tell what EA account it is using on Xbox child account

Hi,

I'm pretty new to consoles. I play on PC and have been playing Fortnite and Rogue company with my son, with me on PC and him on his switch. I bought an Xbox Series S the other day and I'm trying to set it up so we can play Apex Legends.

I already had an xbox account as I had the PC version of the pass and app so set everything up on the new xbox with that account.

I created an xbox child account for my son although other than communication, it is mostly unrestricted. This shows in my Xbox family app.

I added Apex legends onto the Xbox and as his xbox profile it loaded up.

There was a message about EA and having to approve, but I can't remember if I had to sign in or anything.

I've installed Apex legends on my PC using Origin, on an EA account that is linked to my Xbox account. I can already see that I have to have a different Apex profile between my own Xbox profile on Apex and the Origin Profile due to some restriction I've just read about (cross-progress?).

I tried to load Apex legends on the xbox on my xbox profile and I had to sign into EA. I don't remember if I did this on my sons which I had done a couple of days before.

I've seen all these posts about being unable to crossplay between Xbox and PC if they are using the same EA account, what I can't tell is what EA account Apex legends on my son's profile on the xbox is actually using, so I'm trying to find out if its the same (and therefore we won't ever be able to play one another and we can just delete the game on both systems) or if it is using another account.

I'm as confused as confused can be. I design enterprise software for a living but can't for the life of me figure out how this is supposed to work. Honestly it really shouldn't be this difficult, Fortnite and Rogue Company was just a matter of adding the other name as a friend and pressing accept, it took less than a minute. 

I'm thinking this isn't possible and we will likely have to give up, if I could just know for sure what EA account that xbox profile was using then I would know that it isn't possible due to another series of quite ridiculous oversights but without confirming that I'll never know. The trouble is I didn't film everything I did every step of the way as I didn't expect I'd have to log my actions to troubleshoot later!

One final note, when my son tried to play online a game with anyone it was limited to xbox only and never completed matchmaking. Also he doesn't have an "Add friend" option like I do on PC. I noticed I'd disabled cross play on his xbox account which I enabled 2 hours ago using Xbox family app as well as not needing my permission to add a friend but a couple of hours later nothing has changed here.

Thanks for reading.