Background is birthday party booked months ago for dd birthday. It's an activity type party that has a start and end time and if anyone arrived late they wouldn't be able to participate in the booked activity.
DSC has a weekend hobby that they are not really that interested in, when asked if they want to go to practice the usual answer is a resounding no! Anyway the hobby has a performance coming up that has unfortunately fell on same weekend as Dd birthday party. The performance itself isn't actually until the following day after dd party but they have a rehearsal they announced this week that clashes with dd party itself. DSC have stated they want to come dd party and not the hobby rehearsal. DSC mother being very difficult stating they can't come to party and have to go to rehearsal instead.
It's DP access day so DSC are in his care yet DSC mum is dictating that they can't come.
AIBU in expecting DP and DSC to miss the rehearsal and come to the party?