My players are in a street brawl in a medium sized city. They are with several royal guards fighting against a gang.

The party is doing mostly fine, and doesn't need more help than they already have to win, but it's still a hard fight (mini boss with several lackeys). One of the PCs siblings knows the fight is happening and is close to allies they can send. My main question is if the allies showing up before the fight is over might cheapen the experience of winning the fight. Should I just have them show up too late help and like "next time leave some for me" or is that going to make the players feel like I let them flounder when help was on the way?