
Puppies need a lot of attention to housetrain and socialise, for this reason most responsible breeders would not consider selling a puppy to a home until any existing dog was mature and at a level of training to allow the owner to devote the necessary attention to the younger. Puppies, particulary toy breeds soon grow into adult dogs and behave as you might expect adult dogs to more than two would take the training and handling skills of an experienced dog owner to prevent the extra problems of pack behaviour something few toy dog owners would enjoy in my experience.
I presume you have dropped the idea of allowing indescriminate breeding between them as you stated in your previously removed thread as this is something else no reputable breeder would countenance.