There isn't wifi on board.
Only one or two of the new trains have wifi and not the whole rolling stock.
If it helps....
Every day there is a Disney train. It goes from London, stops at Ebbsfleet and Ashford to the park direct.
It's full of children. All noisy and running about and excited.
That may help or it may be a total trigger.
If you stay in a Disney hotel, then your case is loaded by staff and taken to your hotel. Really helpful but delays you a little especially on the return to queue to get it back at the station.
Security (to board and clear in France) on the Disney train was awful. Took about an hour, long wait and lots of noise.
Oh and the station toilet has a guard dog like woman insisting you pay to use them. All in loud French of course. She'd upset you whilst you're dealing with DS. Have loads of Euro change at the ready!
Other trains go to Paris central, you would change and use the metro to get to the station to commuter train you out to Disney.
Longer, and very different. But quieter trains. More likely to be a wifi train. Business and Paris tourists. Far less children. Easier quiet security.
Can you board at Ashford or Ebbsfleet (regardless of train)?
Parking is a bit steep but the getting through security bit is a total breeze and so quiet. Really easy and stress free. Still make sure your seats are pre booked and together.
They have lots of tables of fours. And then pairs of twos in rows.
I think your pinch points would be getting in and out the station at Disney / St P and perhaps the buses in and out of the resort hotels.