I kept Lemondrop and Goldie together in the house for months while I was waiting for the weather to warm up enough to move them back into the outdoor aviary.
They have formed a bonded pair and continue to stick close together, even after being transitioned back into the aviary recently. They groom each other, feed each other, sleep next to each other and draw comfort from each other. They are a sweet couple.
Which is not to say they don't argue. Lemondrop is very strong-willed and vocal if Goldie displeases her. I call it her "angry voice" and it sounds like a pissed-off typewriter. Goldie is more of a sweetie and she doesn't start fights as often as Lemondrop, but there are times when she runs out of patience and has to express her feelings in traditional budgie hen fashion. The fights are rarely physical and brief in duration. They make up with each other quickly and don't hold grudges. It is clear to see that they enjoy each others company more than being apart.
If you have a choice, two boys are more likely to be compatible than two girls. And a boy/girl pair will probably also do just fine together, but you will want to have a plan in place for what to do if you get any eggs. Two girls are the most likely pairing to suffer incompatibility issues, because if you get two strong-willed hens together, their personalities might clash too much.
Snowball is a good example of a hen that would be difficult to keep with a hen too much like herself. She is my most dominant hen and everyone knows to give Snowball lots of space and let her just take what she wants. I don't think Lemondrop and Snowball would work as cage mates. They would both want to be top bird and probably argue over every little thing. On the other hand, Snowball and Opal might not work out either. Opal is one of my most passive hens. She might end up being bullied and pushed around by Snowball too much. I would need to be careful to provide enough space and multiple food and water stations to ensure both girls could feel comfortable and meet their needs without too much interference.
Ideally, you want hens that won't clash with each other constantly, but also hens that won't get bullied one-sidedly. Some drama is to be expected and acceptable. You just need to watch out for strong incompatibility and serious violence or risk of injury. Many people have had success keeping compatible hens together for years. Keep in mind, the more hens you keep together, the more space you need to provide, so the birds can keep away from each other when necessary. This is true regardless of gender, actually. Adding more birds adds complexity to your flock dynamics, which can be good or bad - in some ways, it is much easier to keep more hens in a large space, rather than a pair of hens in a small space. Avoid hormonal triggers to reduce territorial aggression, so no nest boxes or coconuts or snuggle huts. Budgies are opportunistic breeders, so your goal is to not give them the right opportunity.
Budgies really do prefer the company of other budgies and they do best with a companion. It is possible to keep a lone budgie, but in that case YOU must be their constant companion and fill the role of a second budgie, to the best of your ability.
