After the suggestion of the other day, few more infos for Yannis.
1- Paleologus: it is the family name in english and in latin when, in fact, this family was ruling the Byzantine Empire - the last family to do it. But in France, where many of their descendants lived, the family name is different. It is Paleologue, with 'ue' at the end, instead of 'us'.
2-I'm french, but quite far away from this country as I've been living in Taiwan for close to 15 years, but, may be, if someone from this Forum lives in France, he can help you to get in touch with the french descendants of the Paleologue. I know there are still some people from this family as I had some in my class and school 25 years ago. For sure, few of them are living in Paris or in the close suburbs around. If you contact them, I'm sure one of them may have some informations.
3-For the order of Malta, the most well known name of the sovereign military hospitaller order of Saint John of Jerusalem, they have a website (
http://www.orderofmalta.org/) and a special status as an independant State that gives the order the right to have a seat at the UNESCO, the Europe council, and few other official organisations, so it would not be difficult to get in contact with them and check with them if the symbols on your sword is from this order, if there was a jean Paleologue as a member before.
Best,
yuanzhumin