This sounds like one of those situations where Daughter, Son and DIL need to sort of their differences between themselves.
Try and stay neutral - the whole thing sounds trivial, but sibling rivalry can be powerful.
If your daughter will be living with you for x days a week, then of course she's entitled to be there those days. It's her home for those days. The same applies the days she's living with her father.
If she's got horses, then, of course, she needs to look after them - animal welfare can't hinge on family squabbles.🙄
You son and DIL can, obviously, decide who they don't want seeing their children. But, they don't get to decide who is in your home.
Not their decision.
If the days clash, then they will either have to sort out things with your daughter, or starting lamming out for paid childcare.
The reality of what they can cost might bring about a change of heart.
But, other than that, stay out of it.
They are all adults.
Best wishes.💐
Giorgia Meloni Gives Trump Both Barrels!



. We are all giving advice and voicing our opinions and it's up to the OP which they choose to take on board or disregard.