The fact that the Northern Irish character is involved, and supposedly claiming the title "Northern Irish" rather the more common British or Irish (as allowed by the Good Friday Agreement), does seem to make me think the character with likely be of the Protestant faith and of loyalist persusasion. I agree with you, a Catholic Republican of Northern Ireland wouldn't be associated with such a team, particularly at this time of political disagreement. The team does seem to be set in the present day, and Captain Britain has already made it clear Brexit was underway (and seemed to lean towards Remain).
I also hope the Choir isn't just willing to go along with everything if this is a political tale amongst an intergalactic threat. Wales isn't as vocal, having been absorbed into Britain during their relative infancy, but they are to be amongst the most harshly affected since EU contribution towards agriculture (and it's trade) assisted their livelihoods. Also, it's no secret that when times have been hard within the U.K. they've often been hardest on those reliant in industry and agriculture (the abundance of farms and coal mines make this abundantly clear to affect Wales). So I hope that she has a voice that is her own, and of her people.