Annie-
About the difference in status between the Yusupovs and Bagrations: There IS a huge difference. The Bagrations were a sovereign, ruling house from the 9th Century until 1801-making them older than the Romanov Dynasty. In essence, this made the Bagrations like any other former ruling house that was considered ebenbuertig or equal for purposes of marriage, even though they no longer ruled: the Bourbon-Orleans family (dethroned in 1848-but remember Alexander III wanted Nicholas to marry Princess Helene d'Orleans); the Hanovers; the Nassaus; etc. All were considered equal for purposes of marriage.
The Yusupovs-and for that matter the Rurikids in Russia (Galitzine, Dolgoruky, etc.) are a different story, as they had not held actual power for hundreds of years. The Rurikid princes were in essence vassals of the Muscovite Kingdom by the reign of Ivan III, and they never exercised sovereign power over a recognized nation state, as did the Bagrations. The Yusupovs, in contrast to the Bagrations, also voluntarily agreed to vassal status under the Moscow Throne, renouncing their previous status as Khans. The Bagrations, though, were forcibly deprived of their sovereign status when Russia illegally annexed Georgia in 1801, in violation of a treaty Catherine II had signed just a few years earlier recognizing Georgia as a sovereign country and the Bagrations as its sovereign ruling house.
That, in a nutshell, is the difference-Rurikids and the Yusupovs were not in the same category as the Bagrations as far as previous sovereign status; as far as ruling a recognized nation; and as far as voluntarily giving up their sovereign status.
Greg King