Great to hear you are upgrading your cage size
your budgies will be delighted with the extra space
As for your concerns about loneliness, extra space is not an issue for loneliness especially seeing that they already have each other. Adding 2 males however will change the dynamics in the flock and should not be done without prior research and preparation.
If they did breed, you will need to have extensive knowledge and resources to step in if anything goes wrong (which it easily can). There is also the added risk of 2 sets of pairs breeding meaning double the care, double the increase in numbers etc.
I definitely wouldn't house two breeding families together which would mean you would need two separate cages for each breeding pair and then either a third or possibly a fourth cage to house the female parents away from the chicks (if needed - i'm not an experienced breeder but I have read that some females can become aggressive towards the chicks and subsequently needing to be housed separately).
There is also the possibility that introducing 2 more might not work out from a personality perspective and they may never be suitable to cohabit.
It is also recommended to keep an even number of budgies as an odd number can cause problems of bullying.
For now I would suggest seeing how your current female pair adjust to their new set-up.
If you really feel the need to expand on your flock, please do a lot of research and look at your overall situation and means to provide for potential outcomes.
Consider cost of equipment and veterinary bills, resources - access to an avian vet and perhaps an experienced breeder to fall back on for support if needed, space in your home (in the event some of them need to be housed separately or if they do breed (by this I mean both in the event of extra flock members (chicks) but also, separating the female), support, overall goal.
On a separate note, I would love to see pictures of your two females
- what are their names?