Non-sovereign nations with World Cup teams

Yes, I know it’s a bit late for a World Cup question, but this thread reminded me of something I’ve been wondering about for a while.

From what I understand, a person has to be a citizen to participate in a country’s World Cup team. But what about when the team isn’t representative of a whole country? For example, England, Scotland, and Wales each have seperate teams, but none of them are countries: they’re all part of the country of the United Kingdom. How do they set the requirements for them? Is it possible to be a “citizen” of Scotland, England, or Wales, rather than just being a citizen of the UK?

Also, the US, Puerto Rico, and the US Virgin Islands (among others, I know) all have seperate teams, yet Puerto Rico and the Virgin Islands are part of the US. Could the US team contract people from PR and VI, since these people are US citizens, or can they not, since these territories have their own teams? And, once again, how do they set citizenship requirements in the territories who compete on their own?

Thanks in advance for any answers.

From the FIFA statute book:

The English and Scottish football associations predate FIFA, so in their case it would probably have been automatic.

BTW, England and Scotland are indeed countries. The terminology does not necessarily imply political independence.

Yes, PR athletes can (and do) compete for US teams, at least in other sports. One of the men divers in the 2000 Olympics US team was a Puertorrican. Gigi Fernández has played tennis (and won gold) while being in a US team.