We cannot advise you on your original post because you want to put all your budgies in one cage. As that implies that all genders will be mixed together, we can't give you suggestions on this because they should not be in a mixed gender situation if at all possible.
The best case scenario would be that you had one cage for males and one for females in a room away from the dog and you went to spend time with them daily. However, I understand that your current resources may not allow you to do this.
The most important thing is to ensure your budgies are
1. Safe from your dog at all times
and
2. Are NOT in any living situation where they may (accidentally or purposefully) breed. So far what you have told us indicates you should not be breeding your budgies. Yes, older budgies often CAN breed, but that doesn't mean they should. There are very few exceptions to this general rule which are always decisions undertaken by experienced individuals and usually with joint consultation of an avian vet. Any person who is willing to risk the health of their budgies and potential babies by breeding older budgies is an unethical breeder who is putting the production of chicks above the health of the individual offspring and parents. Therefore please consider the advise above and continue to do research on how to give your budgies the best life possible; six birds is already quite a lot to ensure you have vet care, healthy food, and space for each one.
Thanks for your understanding why we may focus on a different piece of advice than what you originally asked for. We are a forum dedicated to education and resources for budgie owners that takes all advice from board-certified avian vets and similar level veterinary research and thus make it a priority to address issues we see with people's posts so that not only the original poster but also any visiting forum members can see the most recent advice and recommendations for a particular situation.
