Fit1nho

is spanish actually an ethnicity

It's a bit complex. Spain is often defined as a 'multinational' (plurinacional) nation/state that share main similarities within its borders, but at the same time, there are cultural aspects specific to certain subregions. Spain is a mix of different ethnic groups that existed in the Iberian peninsula through time (celts, íberos ('iberians'), roman, berber (some settled in the penisula after the reconquista) and many others. So you could consider spanish an ethnicity, but galician, andalusian, catalonian, castilian, baske, etc. as well.

and in spain catalonian and basque are totally different languages especially basque

Spanish, catalan and galician (and portuguese, italian, french, romanian) languages all descend from 'vulgar' latin, that is, latin that common people spoke. Catalan in particular is very similar, apart from spanish (often called castilian) to Italian or French. It is spoked not only in catalonia, but in valencia or the Balearic Islands (mallorca, menorca, ibiza, etc.) too.
Euskera (baske) is a compretely different language, it is an isolated language. We don't have evidences of where it came from. There are many different hypothesis, but all of them still unproven