My DGDs have a special bond with their other grandma. She spent a lot of time with them and they get on well. Having said that I know they love me and DH. We have had great times together. Most importantly don’t show it gets to you. It’s hard I know bu they are young. In 6 months or a year things could be completely different. When you have the boys in your own make sure they have fun and a good time and just enjoy their company then. It would be a shame to make life difficult for your DD who obviously feels your hurt but can’t talky do anything about it. Try and not to worry about it. From someone whose grandchildren are now almost adult, trust me things change. Be good caring grandparents and play with them, give them love and support them and they will remember that not whose knee they sat on one Christmas.
Children holidaying during term time.
Do you try to keep childcare (fairly) equal between your grandchildren?