okay, I know not every word that ends with "ь" is to be feminine....we also have to take care of the gender of the person....but if my guest is a woman, can't I say "наша гость" ?? if you say "no, it is always male" then I promise I will not argue back :) if you say "yes, it can be both" , then my answer needs to be accepted also as correct..
The feminine form is го́стья, so you should use «на́ша го́стья».
(But of course mightypotatoe's answer is also true, please don't downvote it. Of course you can use гость to refer to females too, and then it uses masculine adjectives.)
It is the same difference as мой vs. моё, твой vs. твоё. The ending depends on the gender of the noun it modifies. 1st and 2nd person pronouns (and also the reflexive свой) have a pattern similar to the one adjectives use. Ваш and наш have the same endings, also мой/твой/свой have the same endings.