Apparently some mobile phones do allow 2 sims to be active at the same time. However as an Apple user, I can only use 1 sim at a time. That shouldn't be too much of a problem as basically the only time I'll need the UltraMobile sim active is when I'm at my desktop doing some financial functions.
If my Thai mobile carrier allows it I could forward my inbound calls to my wife's phone while I'm using the UltraMobile sim for a 2FA message or call.
Info on dual sim phones, etc. found at:
https://www.techadvisor.com/article/723395/best-dual-sim-phone.html