If you only have two birds, and you got a white and a brown egg, you have two hens. The only other option is someone is playing a trick on you. Roosters don't have ovaries.
that may be a possability someone putting store eggs into the nest box, esspecially if you say you have only 2 chicken as they wont know where to lay the first eggs unless they are coaxed with fake eggs left in nest box
very rare will you find chicken have layed a first egg in teh nest box when they dont follow others from the flock or have been trained
my chicken would lay every where for about 2 weeks and then eventually learnt the nest box, now all new chicken use the nest box as they follow the lead of the other chicken
I only have two chicken the eggs were in the same nest one was white and the other egg was brown. well if everyone is saying both chickens are roosters then the eggs might have been rooster eggs which are eggs that are not complete which explains the one time deal.
Rooster eggs is a myth, they are called Fart eggs layed by hens (eggs without yolks) (dont worry about that as that is a whole different thing and nowt to do with your being hens or roos)