What Kind of Bees Are These Entering Our Hive?

Hi! By way of background, I'm a retired Marine with less than one month of "bee keeping", though I really don't feel qualified to say that at my stage. We just got a 5 frame Italian nuc on May 1, 2020; our first. Bees have been doing great. Filled up the first deep super in about 2 weeks, then I added another. Today I noticed several larger bees coming and going. They look like honey bees, though larger....maybe a different variety, like Russians or Carnolians? I've read that often nuc sellers have a hard time keeping a pure variety due to cross breeding. I don't think drones come and go like these were doing, from what I've read. The attached photos shows some examples...you can clearly see the size difference. Some of them are darker, and a few are a light amber color. The guard bees don't seem to mind the odd ones coming and going...you can see in the pics that they appear to get checked out.

Our hive sits on 80 acres in a clover field, which is surrounded by about a half mile of forest on all sides...there are no other hives on neighboring properties that I know of. The big bees aren't carrying anything when they leave, though they have the habit of stopping and cleaning their antenna before taking off ,which makes me wonder if they had their heads in a honey cell. I hope I just have a hybrid hive, and that this is not robbing.

Anyhow, thank you for your help.