Both your husband and his daughter sound absolutely awful.
Both happy to use you though.
I mean it kindly but you sound like a bit of a doormat who chose very poorly in your husband that he would allow you to be used and treated so poorly.
My friend was in a not dissimilar situation last year.
A step daughter who has been a cool distant person for 20+ years.
Not rude, but never warmed to my lovely friend.
My friend retired shortly after her husbands first grandchild arrived.
After about 4 months into her retirement her husband mentioned that his daughter had asked for "him" to mind the baby.
My friend was very calm and told him that it was his choice if he wanted to, but she had plans for her retirement and childcare was definitely not any part of it.
Her step daughter returned to teaching last September and my friend booked a serious of cheap holidays in the sun with anyone and everyone and was away more than she was home.
Her husband was stunned as he really thought she would just do it.
He was very upset.
After one month he told his daughter it was too much and he felt completely tied down.
Unfortunately she was unable to find alternative care easily so the arrangement went on for 6 more months with him doing 3 days a week rather than the 5.
My friend got into serious training to do a huge Camino walk for 3 weeks with a group of friends and this also took her away very regularly on short walking trips, long days out.
Her husband was very sore with her until she asked him would he like a divorce as she had zero intention of tolerating his efforts to guilt her about enjoying her retirement, and she really meant it.
The did some counselling and are finally doing better after a very rocky year.
My friend is very gentle but she has a steel core that he now has finally fully witnessed.
She will not be used.
She has actually said it was a bit of a blessing as it forced her to really look beyond her relationship in her retirement and that has been great.
OP, there may be more grandchildren to come, so being very firm now is in your own best interests.