I'm familiar with the brothers you speak of and have had a really nice conversation with the "pruder" of the brothers, who I find really attractive (probably moreso of the two). Overall I think that everyone in this situation is old enough to understand what's going on. If you're not forcing them to do anything they don't want, then everything is a-ok.
What it comes down to: is this something that you're going to feel odd or unhappy about after the fact? If you have hang ups about it now, maybe you can visit other options instead. See them during separate sessions? Do you just want to see them at the same time so that you can say you saw two brothers at the same time? If that floats your boat, then sure, but at the end of the day it's about what will make you the most comfortable or happy.