With regard to the gypsy subgroups (mentioned as possibly related to Indian castes above), see https://en.wikipedia.org/wiki/Romani_people#Romani_subgroups (I cannot vouch for the level of accuracy but it seems like a start). One presumes that they share a common genetic and language heritage stretching back to their Indian origins; certainly some of them look strikingly "Indian" in features once your mind is attuned to that. The main gypsy group I am (semi) familiar with - mostly at second hand - is the Manouche of France, called Sinti in the Netherlands and Germany - according to whether they speak French or Dutch and German in their main "adopted" homelands (but they travel across country borders), different from the Gitans of Spain (responsible for flamenco) and also maybe from the musical gypsies of Hungary; this is the tribe/group responsible for the "gypsy jazz" of Django Reinhardt etc. As the article says, Manouche/Sinti consider themselves "different" from the other Roma, to the extent that (e.g. in Germany) then greater ethnic group is sometimes called "Sinti and Roma". Getting a bit off topic maybe, but part of the bigger picture.

I imagine that those English Roma whose trade is mostly horse dealing could be related to the Lovari (Lowari) sub-group, horse dealers in the main, as identified e.g. by Jan Yoors of Belgium, who as a boy travelled extensively with them in the years preceding the second world war.