You should at least get the male neutered soon. That will take care of a second unplanned pregnancy once the babies arrive. Then get the female spayed once she recovers from the pregnancy. Or goes into heat again and gets obnoxious.
A stray adopted me and it turned out she was an unwed teenage mother. She went back into heat when the babies just 6 weeks old. The babies were even still nursing some.
And enjoy the babies. It is wonderful to watch them grow. It is great that you have homes for them. The hardest thing for me was the worry of finding them a good home. I even turned down 3 people because they just did not feel right.