Sorry, gotair?, this just seems dumb. Why add another point of failure with a splitter?
Get your wife another Uwatec and just pair it as your Sol's "buddy" xmtr and as her primary xmtr.
I don't mean to be offensive, but it sure seems awfully controlling of you. If it was a child, I could understand, but an adult? Seriously?
I am not really into having another failure point, which is one of the reasons I started the post. Just looking for other opinions or ideas. As far as being controlling, lol I don't think I am but others might see it as being controlling. So jax, am I to understand that you never ask your buddy how much air they have?