How am I supposed to know, if we are talking about one or more mothers and fathers? I know it says "your", as in belonging to more than one person, bit these persons could be siblings, and in that case, wouldn't it be the exact same sentence, but meaning just one of each type of parent?
Wasze is plural Yours (more than one owner) reffering to a singular Neuter noun OR to a plural noun that is either Feminine, neuter or masculine (not personal tho, i.e. a dog). Wasi is the plural Yours for a plural masculine personal noun. And both Wasze and Wasi are have same spelling in accusative and nominative. So you have it easier at remembering it. I hope this helps.