Hi there Brenda,
I have been doing some digging on this one for a while. You are right to see that there are 2 different Polly's in Amherst, VA at pretty much the same time. It does not help that the families (Beverly and Pinn) run so close together, sometimes merging and crossing at really weird places. I scratch and shake my head every time I think of it too hard.
The Polly who married Richard Tuppence in 1829 is Polly Pinn, daughter of Turner Pinn and Joice Humbles (if you go by just the information on Ancestry, you will get it wrong. A lot of wrong information is being past on this line. Make sure you look at their references). Polly Beverly the mother of Aldridge (1830), Lucy (1835), Anthony (1835), Elizabeth [Betsey] (1835) [twins run in the family :)], Henry (1845), and Herann (1852) is the daughter of William Beverly and Edy Pinn. Edy Pinn was William Beverly's 1st wife. His 2nd wife was Judith Sparrow. I too have not found the husband of Polly Beverly, but I have a few guesses. They are probably wrong so I will keep them to myself for now. I will share this though (I'm fishing for information myself), I THINK that Edy Pinn had two more children Bailey Beverly (1815) and Delilah Beverly (1812). I do not have proof of this yet. I can say that in 1860 the Census says that they - Polly, Bailey and Delilah - lived together. Also on Buckingham, VA Census the names are always close together. I could be wrong though.
You are probably looking for proof that Polly Beverly was the daughter of Edy Pinn. This is what I have - On the 1880 Census, Charles and Judy Beverly (son and daughter of Polly Beverly's son Aldridge) lived with John and Martha Pinn. John Pinn is the first son of Richard and Polly Tuppence. The reason he does not have the Tuppence name is because he was born (1826) before Richard and Polly got married (1829) so he was given the mother's maiden name - Pinn. Again, Polly Pinn (wife of Richard Tuppence) is the daughter of Turner Pinn and Turner Pinn is the son of Raleigh (Rawley) Pinn. Saying that, Edy Pinn is also the daughter of Raleigh Pinn (I warned you these family lines run close :).
Remember I said that William Beverly had 2 wives? Martha Pinn (wife of John Pinn) is the daughter of William Beverly and his 2nd wife Judith Sparrow. On the Census it states that Charles and Judy Beverly where cousins of John and Martha Pinn. The only way, with the information I have, that this could be possible is if Polly Beverly was indeed the daughter of Edy Pinn.
I'm not sure of Evelyn Beverly (Giles). I have not seen that name pop up in this tangled web. I'm not saying it's not there, just that I haven't seen it. Do you have more information concerning Evelyn?
Hope this helps. If you come across more information do share :).