No, if the kids live with you then they don't have to accommodate her. Tell her that this is their normal bedtime and that she is just going to have to arrange for them to have quiet time after her kids go to bed.
Good Lord, even 9pm is pushing it for kids this age. 8:30? Seriously????
I would just look at her incredulously, with disbelief, and ask her how she blacks out the windows to make is appear dark, how does she keep the kids from sitting on their beds watching the neighborhood kids playing outside in the sunshine, that your kids are outside playing while the sun still up, etc...
She is going to face a lot of issues in the near future. Little kids go to bed that early, these preteens are nearly old enough to have summer jobs. Sonic in my area will let a 14 year old be a car hop but not anything behind the counters. There are other places too. They can't work where they have to handle any type of equipment like fryers or pop machines but the can transport the trays to and from the cars. They can work as teachers assistants in child care, etc...a 14 year old child can work a few hours per week. They are old enough to know when they are tired and want to go to bed.
The best she can do is allow them to have a movie on in their room quietly, reading time if they love books otherwise it will be a battle of boredom, watch TV quietly, be on the computer, etc...there are lots of quiet activities these kids can do.
Her kids evidently need more rest since they are used to it. The only other option is to go each day and pick up the kids by 7pm so she can have her regular bedtime routine.
If she goes to work early in the morning she may be struggling to get in bed by her regular bedtime and lack of sleep will make a mom very cranky...lol.. If the kids are willing they could compromise some. They can lay there and write stories in their minds, day dream, work out issues with friends, spend time praying or writing song lyrics, as long as they are quiet and not keeping the other kids awake.