Welcome to the forums, Paul!
You have certainly come to the right place as you will find all you need to know on budgie care here.
If you don't mind, I will start by asking you a few questions first:
Are you relatively new to budgies?
Did you get the 4 budgies from the same place and if so, are you sure that there is no chance for them to be related?
How old are your budgies?
Are your two pairs currently housed on the same cage?
Before taking the breeding route and in order to do so more safely, a person should have a very good grasp of the species (this comes with real life experience in budgie ownership) and to do the required research into the subject.
The decision to breed comes with a whole lot of responsibility and commitment, the lives of the breeding pair(s) and the chicks are depending on you and the response you give if/when faced with adversity.
Things like being able to tell if your breeding pair is in good health and top physical condition to go through breeding; when a hen is expecting an egg or if she is showing the first signs of being egg bound; when a chick is having developmental problems, not being fed or showing signs of dehydration;
when there is aggression, abandonment and neglect of the chicks and it's solely up to you to feed and raise the chicks. The ability to detect early on and solve these issues can truly make a difference on the outcome of your breeding journey.
Please read this link: https://talkbudgies.com/budgie-breedi...s-new-old.html
To answer your question, it's normal for the male to spend time on the nest box with his mate.