This was one of those times you sort of wake up on the couch in the middle of the night and start watching whatever is on the tv.
This may have been an English movie, but I’m not sure. They just seemed to dress very posh I think. But yeah, there are siblings who take a boat out and discover an island. I think they pretend to be pirates as well. Eventually, they come across these girls who said they claimed the island first and they get into a bit of a fight/argument over it. Then somehow they all become friends and solve a crime or prevent one? I don’t believe that the movie had any known actors in it, and I think it must have been made in the past 10 years. I probably watched it around 2017ish. The eldest sibling was a boy who was actually the right age, 17 maybe. I can remember looking him up afterwards but I don’t remember his name.