Need air compressor/tool help!

Unless you're doing continuous work, like running an air grinder/sander or blast cabinet, it's the pressure that does the work for you...if your unit can make 90 psi, you'll be able to do a number of things, maybe just not for long..

Your small unit will be great for staple/nail guns, a small air drill, and of course, airing up tires, pool toys etc.

Your brother's unit would be better suited to running an impact, 1/2" air drill, die grinder, etc. You can run them on yours but just not for long (combination of low cfm at a useable pressure and small tank)

In the shop, I use electric tools for most sanding/grinding work, except for a die grinder, which is air. I use air mainly for running drills and impact wrenches. I'm still using the same compressor I started the business with back in the 80's, a single-stage twin CH with 60 gallon tank. I replaced the 5hp single phase motor with a 3hp 3phase motor and it works a whole bunch better...other than running a sandblaster/blasting cabinet efficiently, it's done everything I need, and I use it every day.