I'm not an expert, but through lots of reading I think I can at least begin to steer you in the right direction.
Q #1. A buck will sometimes stick around a doe for a short time after breeding with her, but would probably be lured away from her by the scent of another hot doe in the area.
Q #2 & #3. A doe is only accepting of breeding for about 24-48 hours and will often allow multiple bucks to breed with her in this time frame.
Q #4. Not totally sure on this one, but I would assume the more dominant buck would flex his muscles and chase the less dominant buck off, but there's no guarantee the less dominant buck won't hang close by and attempt to breed with the doe later on, as per my response to Q #2 and #3.
Q #5. Doe #1 may have already been bred by buck #1, and if it is indeed a couple days later, she will no longer be receptive to bucks. She may or may not still be exuding estrous scents at this time. In all likelihood, she will still smell "hot" for at least a short time after she comes out of her peak estrus period.
Q #6. I haven't heard of a whitetail buck keeping a harem as you describe. A dominant buck will definitely try to chase off less dominant bucks, but he will not keep a harem of does like a bull elk does.
I hope this helps a little. Like I said, I'm not an expert or a biologist or anything, so if anyone else has some more information on the subject, feel free to chime in. I'd like to see some more opinions on this either affirming or refuting what I've said.
Can I ask why the mature/dominant bucks have been placed on a "no-shoot" list? Is it to make sure they get the chance to breed and pass on their genes? Eventually, as they age, they will no longer be the dominant bucks in the area and may be run ragged during the rut and could even get chased off your property, either by younger more verile bucks or by the other bruisers. 300 acres doesn't seem like all that much for 3 mature bucks. I'm not too familiar with "low-fence" properties, so I'm not sure of the extent to which they are capable of keeping deer in/out.