My female is very prone to sebaceous gland cysts.
She has 5 of them atm, 3 smaller ones that look like your dogs and 2 bigger ones that look exactly like the picture qbchottu posted above.
I get my Vet to look at them every time we go in for something and I just keep an eye on them myself. So far they have not changed, if they ooze a bit of gunk, I just clean them with a bit of betadine (iodine) or peroxide (LOL the peroxide bleached her black fur tho)
The one on the bottom of her tail will likely need to be removed soon, the Vet was concerned that there isn't a lot of tissue to work with so she didn't want it to get too big.