Well. I think the answer is two fold.
1) Rumple and Belle aren’t married
2) Rumple’s isn’t actually a Prince.
In all cases before ONCE, the Prince was an actual Prince. Rumple just took over a castle (rather large estate) and set him self up as its master. He’s not actually royalty.
So in this version Belle is the daughter of a nobleman, not a merchant and Rumple isn’t a Prince.
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