Hi Paul
I am a member of a website called Puppy Love. Many of the members there have had puppies from sources similar to yours and have described their experiences, some of them really bad.
I would be suspicious of anyone who could not provide papers to prove the necessary -*test*-('")s had been done. You do not want to set yourself or your family up for heartbreak. There are so many genetic illness that can be passed on, and once the puppy is settled into the family, it's too late to complain. You might not be emotionally able to give the dog back.
So check out as much info as possible to enable you to make an informed choice. And don't be afraid to ask the names of several previous buyers to ask if they have had any problems. If he refuses, he is not as up front as he appears and may just be a hobby breeder.
And although tiny puppies are adorable, that stage is short lived. I promise you a young springer would give you just as much joy in your lives and you would not have to go through the puppy stage as much. Please consider it. You can always add to the pack once the first dog has settled in and bonded with you all.
As for two puppies, well we all have our own preferences on that one
I believe that with two tiny puppies together at the same time, they might bond more with each other, whereas a single puppy or dog is more likely to bond with the human. As Fuddles said, you might have to train them separately depending on what you want them to do.
But that is only my opinion. And I know many members on here have twins and have done extremely well. It's all a matter of preference.
Good luck with whatever you decide.
Cath x