If you are keeping the boys outside (and inside), I would make sure that they are kept quiet and warm, until their post op check, and make sure they are both eating and pooping. For the girl, I would make sure she is kept warm and pain free, and again is eating and toileting, it is a much bigger op for a girl. I would keep them on towels rather than shavings/straw/hay so the wounds aren't irritated and offer them hay in a hay wrack. Remember, DO NOT STARVE THEM BEFORE THE OP.
For you dog, DO starve her 12 hours before the op, afterwards keep her quiet and warm, and on strict rest. I is amazing how many people let their dogs run around a couple of days after being spayed, and can't understand why the wound becomes inflammed or the stitches burst. It is a major operation. Feed her a light meal when she comes home, but don't worry if she doen't eat until the next day.
I know how worrying it is but if you follow your vet's advice and call them if you are at all worried, they will be fine.
Let us know how they get on.