I've been looking into this because I'm curious. Probably won't end up doing it because an angelfish and a gourami in a 26g would be pushing it, but does anyone have experience with these two fish in a smaller sized tank? (as in, less than 50 gallons or so)
I kept a single angel in a 29 gallon with some cardinals at one point. I wouldn't really recommend it, since looking back, that fish probably wasn't super healthy. The tank size wasn't the only issue, but it was a big part. I'd say 29 bare minimum for these guys, and a 40B recommended. Everyone will give you a different opinion, though, so be prepared to form your own opinion by researching.
There are many, many different types of gouramis. A dwarf gourami will do alright in a 10. So will a honey gourami. However, Powder Blues will probably need a 20 long minimum.
Honestly, I wouldn't keep both of those fish in a tank smaller than a 55. They're both what I'd consider "semi-aggressive", and might be a bit more inclined to kill eachother in a small space.