Welcome to BYC!
So, all your birds are 30 weeks old?
FYI...they are called Pullets and Cockerels until one year of age, Hens and Cocks(or cockbirds or roosters) after one year of age.
2 cockerels and 9 pullets.....might be 1 too many boys, depending on their demeanor's.
Young cockerels can be pretty exuberant, and multiple males creates an environment of competition which ups the mating/dominance activity.
A 'good' and mature older cockbird will not mate a female that is not in lay,
most cockerels will often mount anything they can as they just don't know any better yet.
Mounting is also a dominance/submission behavior...if she is letting them mount her, it may not be to mate.
Does your girl in question have all the signs of laying?
Signs of onset of lay---I've found the pelvic points to be the most accurate.
Squatting:
If you touch their back they will hunker down on the ground, then shake their tail feathers when they get back up.
This shows they are sexually mature and egg laying is close at hand.
Combs and Wattles:
Plump, shiny red - usually means laying.
Shriveled, dryish looking and pale - usually means not laying.
Tho I have found that the combs and wattles can look full and red one minute then pale back out the next due to exertion or excitement, can drive ya nuts when waiting for a pullet to lay!
Vent:
Dry, tight, and smaller - usually not laying.
Moist, wide, and larger - usually laying
Pelvic Points 2 bony points(pelvic bones) on either side of vent:
Less than 2 fingertip widths apart usually means not laying.
More than 2 fingertip widths apart usually means laying.