I have two hives right in my backyard in town. One very large and one moderate sized, No problem at all. Unless you're standing within ten feet of the front of the hive (and therefore in their flight path), you'd not know they're there.
We had a dozen people for lunch on Sunday, and ate in the backyard about 20-30 feet from the hives, no worries. The trick to that is simply that our picnic table is across the yard by our garage and house - the bees have already flown well up to clear the buildings before they reach our side of the yard, thereby missing all the humans as well.
We could easily put up a 'fence' to encourage the girls to fly higher even sooner, but realistically we wouldn't really use more of the yard than is already available to us anyway.
It's not a bad idea in a residential area to pick a spot that it 'out of sight, out of mind' for your neighbours, and make sure the girls have a water source handy, but other than that.. go for it.
Oh, and if the issue is having two hives versus just having one, look at it this way: having two hives gives you the ability to be more aware of potential problems with either hive by comparison, and the means to address those problems quickly and easily (availability of brood, stores, etc).. all of which means happier, busier, calmer bees.