People still don't seem to get it.
The use of "Roman Catholic" was British imposed, as they were of the view that the CofE was "Catholic", and hence was a "Catholic Church".
Internally, the Catholic Church is simply the Catholic Church, and many clergy resented the English imposition of "Roman Catholic".
Not entirely. Not really about the 'hated English' per se. Perhaps about any protestant religion
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You might wish to edit your post. Did your grandparents really have a same-sex marriage at such an early date?

I don't think it was the "hated English", so much as a Protestant church and country imposing a name on their own (Catholic) church, a name not of their choosing. [Though the two concepts admittedly overlapped].
While there were many aspects, the determinative one was probably the legal one. For many years if you left a bequest to, say, the "Catholic Church" it wasn't going to go to who you thought it was going to go. It would go to the established church instead. Likewise, British official documents, army, navy, etc. all insisted on the use of "Roman Catholic". And GRO documents too - which is how we got into this discussion.