Without more info hard to be helpful, but I will point out that adoption is a
valid link in the line of descent if you're looking to establish a clan connection.
Also, non Scots do join clan societies simply on internal feelings of affinity,
and many are members of clans simply because they approached their choice
of chief and said I want in if you'll have me. The membership is who the chief says it is. Period.

On a relevant note, one of my lines is a Ross/Rose one. Both spellings in several generations. Clan Ross says if your name is anything like ours, or even if it isn't, join our society, pitch in , help out while you get your genealogy sorted out. You'll meet some great folk, have fun, maybe you turn to be ours. Maybe not. Then you can decide all over again. I find that a lovely attitude.