I have right now 2 budgies, 2 cockatiels and 2 linnies in inside aviary and they get along very good. But it was a long process.
Kids and tiels was almost from the beginning together. Linnies was rescued last year and they was in the separate cage.
My first attempt for putting linnies inside aviary was to fast(I believe it was 3-4 months after they came). Linnies just stayed in the corner and was even afraid to move far away from each other. After couple of days they came back to their cage.
Couple of months later I realized that birds from aviary and 2 linnies in the cage are contact calling each other more often and more often. Then I risked again and ta-da, it worked this time.
At the beginning all of the birds established who is the boss, but there was not real fights between them.
More: at the beginning linnies was shy, but moving there and kinda following the rules of budgies. Tiels was friendly. Now I see that linnies start to take advantage of the situation
And the story about Mango (budgie) and my 2 linnies (Venus and Mars)
Mango was my oldest budgie and the first one. He was rescued and if there is real love existing, that bird wanted to take care of every new bird who joined the flock. He was never bully. So when the other 3 budgies(I had more of them at that time) was bossing around linnies, Mango did exactly opposite. He start going between them, grooming them, etc. Very often I saw 3 of them sleeping together on one perch. Very soon I saw Venus (the female linnie) grooming Mango (the budgie). First I was concerned that Mars (the other linnie) will be left alone, but no, the 3 of them started to groom each other, Mars-Mango, Venus-Mars, Mango-Venus.
That was the perfect bird triangle.
Mango was old budgie and he was getting weaker and weaker fast. We check him at vet and we realized his time is coming. Mango couldn't defend himself. Other budgies start bulling Mango and to my surprise my both linnies stood brave against the budgies, they didn't let no bird to hurt Mango!
Mango died, but to the end linnies was with him, grooming him.
I thing that with different species of birds it's a bit of hazard, luck and a lot of patience. Look, my first attempt to have them together was too fast, but later they got along (sometimes even too much) Timing was wrong. Now Mars the linnie is trying to be louder than Mickey the tiel in the morning. It's really funny how they learn from the other birds.
Good luck with whatever decision you made!