Apostille civil documents for the consulate (birth/marriage certificates and other foreign public documents) — under the 1961 Hague Convention; each document must be apostilled in the country that issued it

An apostille is the international "this document is real" stamp under the title's Hague Convention — and the rule that trips people is in the title too: each document is apostilled in the country that issued it. Order certificates fresh (consulates dislike old ones), get them apostilled at home, and only then translated. Doing this from inside Spain is possible but much slower.