Do you babysit for free? If not, that cost plus the cost of gas, is it worth driving 70 miles to a job?
You raised your family and it's her responsibility to raise hers. It's her boyfriend not husband. She's in a situation she chose to have, not you. Where's his family?
You have helped her for 7 1/2 years and she needs to apparently be reminded of that. She chose to work nights, not you. You were not asked before the decision was made. It apparently was a "taken for granted".
I would just tell her that you have watched your grandchildren all that time and love them deeply just as you do her. However, his children are not your responsibility. Where's his family? You have given all that time for her. You are not being selfish but it was her decision to take this job.
Lesson learned -- we have to take responsibility for the decisions we make and the consequences. She made the decision to work nights and she needs to find the babysitter. She can check with daycares where perhaps one of the workers would be willing to work nights. She can advertise.
If your husband works days, then that simplifies it some in that the evenings are for him to relax or the two of you to do things together - not babysit, especially 4 children.
I wish you the best.
Lynn

I totally agree with Lynn. This was HER choice. I've had to do the same thing with my daughter... Stick to your guns and make no excuses, you have a right to make your own choices just like she does. And you don't have to even listen to the guilt trips because that builds her sense of entitlement. Be strong - she'll respect you for it someday. Hang in there! Nancy

I agree. This was a decision she made without your input. She simply assumed that you would alter your life and continue to provide what I assume is probably free babysitting. Why would she take a night job anyway. Even if you do watch the children while she is working, they will be sleeping. While she is sleeping during the day, who will be caring for those children then? Watching a lively 3yo, getting the older ones to school and back? Or is this night job over at midnight and she will wake up the children in the middle of the night? She is the selfish one. And she and the boyfriend have been taking advantage of you.

Say NO. Stay strong. Stick to your guns. Don't put your marriage at risk. It will be rough, but She needs you too much to turn away.

I agree, stay strong and maybe it would help if your husband is beside you when you say no. some times when there is a third party in hearing distance people control them selves better.

Her crying and yelling that you're selfish and only care about yourself is her projecting. That's deep down how she feels about herself and she's trying to feel better about that by finding a reason to blame you for that same thing.
Saying no is not unreasonable. She's the parent not you. She need to get a day job.