Double factor is not a thing in whiteface mutations. No such thing. I think what the previous owners are trying to say is that both birds are VISUAL whiteface (obviously lol) meaning that if bred together they will only produce whiteface babies. You breed either one of them to a normal bird and you will get a normal baby split to whiteface. Whiteface is a recessive mutation like pied and both parents have to carry the mutation, whether they are visual or split to it, to be able to have babies that are visual as well. So what they could mean is that their parents were also whiteface birds as well. But no, in cockatiels, there is no such thing as a double factor whiteface. Double factor is reserved for mutations such as silver, which I have never worked with.
These parents only produce whiteface cinnamon babies because they are both visuals of those two mutations. Honestly, I wouldn't pair them up myself, as there's too many similarities going on for my taste and I'd be worried about healthy babies in the nest.
Thanks DallyTsuka for siggy!
Snowball-whiteface cinnamon cock
Jeep-normal gray cock
Pebbles-whiteface pearl pied hen
Pankakes-PF cinnamon pearl pied cock