If the boys are getting interested (sniffing and licking and chomping their lips ;-) ) then she is close. If you can give her light coloured bedding to sleep on you should see drops of blood when she gets up. You could also start to wipe her vulva first thing in the morning just after she has stood up with a tissue. Again drops of blood should appear on the tissue. Unless she has a silent season where she doesn't bleed

:-)
Her vulva will swell to double the size it is now (maybe even more as it's her first season) and will become soft and spongy as she nears her peak. She must be kept away from the boys during this time. She is far too young to be having an accidental (or otherwise) mating and litter.
As far as the boys are concerned you are going to have your hands full for a while. They will start to go off their food, might start singing to you (well, to your girl actually :-D ) and will not be as well behaved as normal. They might even start fighting. :-( This will pass as her season ends. Hopefully :-)
Unless you can separate them the whole time it might be better for all concerned to have either the bitch or the dogs put into temporary accomodation. i.e. family, friends or kennels. Good luck.