Late Drop off WARNING VENT!!

So my sister in law texted me at 10:30 last night tellin me her boys would not be there first thing in the morning. That was fine.. 10:30 comes and she knows that's quite time. She tells me her ex husband is going to bring the kids after he has a shower. I ask her if he can hold off til 12 because I don't want to mess up the routine for the other children. ( her kids are really loud and don't listen well and would wake up the other kids) she says that he might have an appointment so she's doesn't know if that can work. So I said okay bring them but just in the future please drop them off before 10:30 or after 12 to avoid messing with the routine. Then she says well see!! I asked her what she ment and she said " well we will see what he decides to do"
People need to understand its not just their kids I'm caring for! I'm not about to make other kids cranking all day just because you ex husband wanted to sleep in!!
What would you do??

I work with the parents when they have an appointment involving their child, but I do stipulate what time they can return their child as I will not wait for them.
Your SIL is out of line here. You have your schedule/routine and she doesn't respect it. The "we'll see" comment after you have explained your schedule needs unminds you and is disrespectful.
You have told her the time frame they can come. If they show up outside these times I would not answer the door. Obviously they don't respect your words so maybe they will respect this action.

So, here's where you went wrong in my opinion. She called and you said 'could he bring them after 10:30' What you should have said was "Well, quiet time is at 10:30 so the kids wil either need to be here before that time or he will need to wait until 12 to drop them off" Your wording starting a discussion and suggested that she had some say in the decision.

The whole... working with our friends and family aside... Our wording is everything. We need to tell them not ask them if it's ok.