My UK citizen son has lived in Poland for 2 years with his non-eu wife of 2 years. He has been offered a job in the UK - what visas will they need, to return together to U.K., please?
Your son doesn't need a visa, of course. His wife can use an EEA family permit if they'll be moving before Brexit. Otherwise, she'll probably need a regular family visa, which she can use anyway, but this route is thousands of pounds more costly.
The ability for family members of UK citizens to use the EEA regulations to enter the UK depends on the Surinder Singh ruling. The UK's interpretation and implementation of that ruling currently requires the UK citizen and family member to have made their "centre of life" in another EU country, to have resided there together, and to have integrated there. I do not know what criteria they use to judge integration, but your son and his wife seem to have met the other criteria.
Some of this, including the "centre of life" criterion, is clearly inconsistent with the EU directive, so if the initial application is refused, an appeal might be in order.