I would not call these napkins "common", but they are not that rare either. Remember that literally hundreds of them were made at a time. As each Grand Duchess or Grand Duke came of age, each was then entitled to and provided with their own personal services of porcelain, silver, napkins etc. I have pieces, for example, from Alexander III as Tsetsarevich, with his cypher of "AA" for Alexander Alexandrovich. These things would have been used for tea or meals where the family was not together at table. Breakfast for example.
I have seen five or six of these Nicholas II napkins on the market, and the Romanov descendants have them as well, since many dozens were in the trunks sent to England after the murders in Ekaterinburg. They sell for about 400-500 each. The Olga Nicholaievna napkin did also probably come from Xenia's things. They were in the trunks from Ekaterinburg as well. They are scarcer and probably would fetch $750-1000.
AP, please contact me directly about disposing of your collection. I am always looking to add to my collection of similar things, and prefer private party sales over dealers.
Best.
FA