in latin, do all words within a sentence need to be the same declension or can they be different declensions?

They can be different declensions.

Explanation:

A declension is simply the "family" that a noun belongs to - for example, the noun lex, legis (law) is part of the 3rd declension and the noun portus, portūs (harbor) is part of the 4th declension. There is no rule in Latin that all the nouns in a sentence have to be part of the same declension.

c. indicates the aid for which you qualify, and allows you to choose what and how much to accept