Do not introduce them until the kittens exhibit more independent behavior! I'm talking like....over 8 weeks old and weaned from Mamma.
I brought in a pregnant female who was friendly with ALL my resident housecats (8 or 9 at that time) but when she kittened, she turned into a she-devil towards the other cats so I kept them seperated!
As a matter of fact, I never let her or her kittens mix with the other housecats until after her babies were taken to the adoption place. We wound up keeping her (Shadow) because she did not do well at the adoption weekend.
Several weeks before the adoption weekend, I had a calico manx bring her two kittens to my house. The babies were wild, and about 9-10 weeks old, the mother (CalicoBob) was people-friendly and she and Shadow got along well. Shadow had just had her kittens taken for adoption so they were gone, and after a few hisses, she and CalicoBob got along famously and both 'took care' of CalicoBob's two kittens.
CB's kittens tamed quickly and when all four went to the adoption weekend, everyone was adopted but Shadow, who hid behind the litter box the whole weekend. When I came for her on Sunday afternoon and spoke to her, she ran to the front of the cage and pushed her paws out towards me, meowing. The care-giver/volunteer was amazed and said that was the most movement she'd seen out of Shadow all weekend.
Kenny and I decided to keep Shadow since she was so traumatized by the adoption cages...she is a lovely kitty.
Anyhow, mother instinct will cause this nursing mother to try to attack your male cat to protect her babies. I'd wait until the babies are much older before introductions...and if you do introduce, do it carefully and as controlled as possible! Mamma may get wild all over him and he won't know why...