I think the pet store question was meant to point out that they are unlikely to be pure bred Cambells and are more likely to be hybrids. They could also be siblings which can mean more problems with the offspring's health
Certainly it is recommended that you assume that they all may carry higher risk of diabetes and feed them accordingly. You may also want to watch them more closely for signs of this.
I hope Sylvi can cope with the second litter when the other is still so young...and if you do not remove Lennon before that litter is born then the risk is of a third successive litter I am afraid :/