If your employer can't be flexible on having leave in hours (I've had jobs in the past were it's a day or nothing), can you take the day then in the holidays look at either a holiday club (a local nursery does school holiday club as well), as you mentioned one set of grandparents who live a distance away, if they could visit for a week to cover holiday time.
Another option is to contact a local college that does either nursery nurse training or teacher training and see if there's a student who would like some practical experience either for the actual training days or the holidays. I trained as a nanny in the 1980s and worked for a family one day a week, I could drive at the time so did the morning school run before going to college, which started at 9:30. I also worked for another family in the holiday doing, one week Monday to Friday 8:00 to 18:00 as both parents worked 45 minutes from the family home.
I would suggest having a chat with any mums at your job and see what they have had re flexibility from your employer, sometimes people assume employers will act in a certain way and they are actually more flexible.
Also does your husbands employer have a HR policy or out of pocket expenses for training.
I work for a large national employer and they will cover out of pocket expenses up to £100 per week for training or trips away. People often don't know about these policies either.
Good luck in what ever solution you find,