Is it por or para on a friend's stupid tattoo?

Todo is correct because it is a noun (or pronoun, to be more precise). If it was an adjective you would change the "o" to an "a". As for the por/para, it cold be either one depending on the intended meaning of the phrase. Using por could mean "All by/through the family" or para could mean "For the family" as in an exchange or as in the tatoo is "for the family"