In particular, Senande, A Cañiza, Pontevedra, is attested as Sisnandi in 934, this being the Latin genitive of the personal name Sisnandus, Germanic in origin; the fist theme is either related to Old High German sisu, glossed as 'carmen funebre'; or either to PGmc *segaz 'victory'; the second theme is *nanþaz 'daring'.
I finally found out one possible root for the germanic -nand: kunnandi=knowledge, huggjandi=wisdom, leikandi=sport, jest. Sisu+nandi, he who knows about the carmen funebre, the ritual funeral singing. I believe nanþaz is a better option, because the ancient peoples loved to attribute glorious, courageous, daring names to their children.
However, there is Bustamante. Boustom is attested in the Botorrita plaques as meaning stable, corral. The very root of boustom, could be from protoceltic bow (bull, cow). This leaves us with the -ante termination. Therefore, while there is a germanic -and, -andi, -ande termination, it seems that there is also -ante, which is probably not germanic but perhaps iberian, celtiberian or celtic? If this is true, what would be the possible meaning of -ante? This is where I got stuck.
Bustamante in my opinion is perhaps (just perhaps) a *Busto Amanti 'Amantius' Farm'; there are comparable toponyms in Galicia: Bustiguillade < Bustum Guiliadi 1038 < *Busto Wiliahathi, Bistipoi < *Busto Pauli, Bistixoán < *Busto Iohanni... Busto is attested in local medieval Latin documents as 'dairy farm', and in medieval Galician as 'herd of cattle'; it must be also related to Welsh bustach 'bullock'.
In any case there is a -ante, -antes suffix present in Galician and northern Iberian pre-Latin place names; for example in the very frequent Serantes, attested as "C(astello) Serante" (ablative) in a Roman inscription; and also in Barbantes (river), Barrantes, Bemantes < Vemantes 1167, Curantes, Marantes < Marantanes 1207, Ourantes… Either they are the result of PIE *-ent- suffix which forms present participles or of *-onts.
Also Bragança < Brigantia, As Anzas < Alesantiam 775 (a river), Arganzo (a river), Arganza (a river), Aranza, Barbanza (a river)…