Tropical Fish In Bags

So about 3 hours in total? 2 hours at your brother's then a 1 hour journey home?

Yes, it can be done. Fish spend longer than that in transit when you buy on line. The thing you'd need to do is tell the shop. The bag would need to be packed differently than for a short trip - some type of ammonia detoxifier in the water (eg ammo lock) and a squirt of oxygen into the bag (if they have it) would see the fish back to your tank.
The problem would come if they didn't add an ammonia detoxifier. Is the shop an hour's drive away, ie quite likely to have different tap water from you? If it does, you'd need to acclimate the fish over a couple of hours. But if there was non-detoxified ammonia in the bag water, you'd have to get the fish out as quickly as possible. In this case, it would be worth having a bottle of something that detoxifies ammonia in your cupboard and add a dose yourself when you get home. It wouldn't need much for the volume of the bag. Your dechlorinator may even do this already, so just add a dose of that.