I can’t speak to what Protestant denominations accept the Catholic Church as Christian, but all my Baptist and Pentecostal cousins and friends accept me as a Christian. In fact, when I’m over at Cousin Wayne’s for a big meal on one of the decoration Sundays, they ask me, the only Catholic in the room, to bless the food!
Not everybody in a denomination would be in agreement on that question. The more “liberal” or mainline denominations have redefined Christianity so broadly, they tend to regard everyone as a Christian who identifies themselves as such. In other words Catholics don’t fall outside their absolute doctrinal boundaries, because they have none anymore. Maybe they would reject a certain person who happened to be Catholic, but not because of their Catholicism.
More evangelical types of Christians nowadays tend not to make Catholicism an automatic rule-in or rule-out, but on a case by case basis. If you, yourself, have accepted Christ as your personal Savior, and believe the Bible, most would say you are a Christian. They might wonder why you also may be carrying around “extra baggage”, those non-Biblical beliefs or practices, but that wouldn’t keep you from being Christian.
A few hard core fundamentalists would say your being Catholic automatically ties you to non-Biblical beliefs that prove you don’t rely on the Bible, and Catholicism is incompatible with total reliance on Jesus as SOLE means of salvation - that Catholics trust in good works, in Mary, and man-made fabrications like the priesthood, papacy, etc. So you definitely aren’t Christian, unless you leave Rome. In my opinion, this group was probably the great majority of Americans a century ago, but is a shrinking minority today.
There are a few extreme groups, which some would label “cults”, that have their definitions of who is a Christian.
Then you have those who are more Catholic-oriented, such as some of those in the Anglican continuum, ACNA, LCMS, PNCC, who regard Catholics as ideal Christians, and see themselves as Catholics who are following a somewhat different ecclesiastic tradition and structure from those who follow Rome. They see Catholics as equally Christian with them.
Then again, maybe your cousins know you are a Christian because they like you. I don’t know what decoration Sundays are, but if that brings cousins together I’m for it.
My cynical side makes me suspect they think Catholics never, ever, pray at all, that you are an undecorated pagan, and they hope by making you say grace you might, maybe, become a Christian.
Don’t you just love cousins? Some of mine make me grit my teeth. And vice versa.