My wife and I travel together, but only have one smart phone between the two of us.
Can I put my wife’s M-Pass information, as well as mine, on my phone?
Would this be do-able in all train stations?

Welcome to Fodors. I don't know the answer to your question. . . . but have you already paid for the BritRail passes? Not always, but very often a BritRail Pass costs more than just buying point to point tickets. Especially with other travel schemes the rail companies offer in the UK -- Like senior railcards (if you qualify) and the Two Together railcard.

So if you haven't bought the passes yet -- maybe hold off and so some more research

https://www.senior-railcard.co.uk
https://www.twotogether-railcard.co.uk

For info for all things train related - check the Man In Seat 61 https://www.seat61.com

Thank you. We have not yet purchased. I need to look into the two together option.

Hint re two together and other railcards . . . You don't need to have the railcard in hand when you pre-book any train tickets. Book as if you had already purchased the railcards, and pay the discounted price quoted. THEN when you are at the station, buy the railcards from the ticket office -- you just need to have them before you board your train. (Same goes for senior or other railcards)

Thanks. I'm a bit confused. To me, "paying" and "buying" mean the same thing. Cultural difference??

"andpaythe discounted price quoted".
"when you are at the station, buythe railcards"

Yes -- the same thing. OK--- to clarify, If you are booking train tickets on-line click that you have the Two Together railcards . . . even if you don't have them yet. The rail card is an actual card that needs your photo attached or, I think they now have a digital version which does simplify things. The issue with the plastic version is they only mail them to UK addresses which is why you'd have to buy it at a station.