UK, Ireland /
From Hertfordshire, UK to Śląskie, Poland - Are we crazy? [35]
the positives probably outweigh all the negatives for all of you as you
I'm in a very different situation than you (tots obvs) but for me the positives _far_ outweigh the negatives (which I'm aware of).
But... how well do you know your mother-in-law? How much have you seen your wife interact with her? I've seen a _lot_ of young marriages have really bad times (or fail) because the parents insist on getting involved and the adult children just kind of... let them.
You have a very established relationship (if you're talking about school age children) but Polish parents, on the whole, are almost constitutionally unable to resist the urge to interfere. That seems like the real weak point (from my point of view) of your plan. And your wife in the UK might be a very different person than she is in Poland living under her mother's roof (lots of international marriages undergo a shock when moving to one spouse's homeland only to see the spouse revert to local ways....)
I'm a pretty different person in Poland than I was in the US (far more assertive, if you don't learn how to be assertive then you'll end up with footprints all over your face). But also I know the language really well and understand how things work (not necessarily what it seems on the surface).
As I always say, it can be great place to live but the learning curve.... she is steeeeep....