Honeybees are loyal to one crop - if there are trees in bloom, they willk work those blossoms until the end before looking for another source. If other trees then come into flower, they will work those.
If you have lots of wildflowers in your area and no trees are in bloom, the bees will decide whether they prefer the wildflowers, or whatever is growing in your garden. They will not necessarily work both at the same time. However, bees from different hives may choose to work different flowers - it depends on what their needs are. Bees collect both nectar and pollen.
Bumble bees will work different flowers at the same time - so for backyard gardens, it is actually better to encourage bumble bees, rather than honeybees. Native bees, including Mason Bees are also great in backyard gardens, they are not agressive unless molested. I have two mason bee nests.
The person who has bees working in the ground --- they are probably bumble bees. Bumble bees come in different sizes.
I think this is true: If you keep bees in your backyard they must be registered with the State. Doesn't matter if it's one hive or many. Honeybees will protect their home aggessively - they are not pets. You will need special clothing and equipment, plus a sterile area to process the excess honey.
Having hives within three miles of your home is a "good thing" wish I had some nearby as I rarely see honeybees here :(