This is the guideline. Each of your images must have something significantly different for the customer. Therefore, they must not be looking closely alike. The three images you have are looking closely alike and would not be accepted if you had another looking like them accepted in your portfolio already. It would have been better if you'd taken the first image sideways and the next from the front to show the origin of the boardwalk and the third as is. This is the kind of difference with similar subject that Adobe is looking for.
We have no idea what percentage of similarity takes into account. If you want to get a rough idea if your assets are similar, drop into the window of stock.adobe.com. There WILL be similars, but you will have to decide for yourself if you should submit or not. In my experience, I've had unique assets rejected, and assets that I would view as similar to many others accepted.
Adobe Community Expert | If you can't fix it, hide it; if you can't hide it, delete it.
I dont think your first question can be answered because Adobe does not inform us what is taken into consideration. To your second question "no". That is not even possible. Like I said we do not know what is compared.