Yea, we only know that the relative is male (as RHD has now confirmed that the rider we are searching for is female in the last set of answers), not that they are a brother. They could easily be a parent, cousin or similar. And that the yes is asterisked raises other possibilities, such as that they were on high level teams but in the era prior to the current system being adopted, or that they were only related through marriage.
So looking at that question about the part of the alphabet the nationality falls into, this narrows things down fairly considerably I think as, bearing in mind this is an Anglophone forum, using the English and native words for a country and it would be way too obtuse to say that, say, Slovenia gets an asterisk because it is Eslovenia in Spanish).
British? (United Kingdom / Great Britain)
Spanish? (España / Spain)
Austrian? (Österreich / Austria)
Finnish? (Suomi / Finland)
Irish? (Republic of Ireland / Eire)