Space is a big consideration. If there is enough, and enough feeding stations around the aviary you may be fine. The concern is that even though your budgies are smaller than the 'tiels, the 'tiels are gentler birds. Budgerigars are more aggressive, and have been known to harass 'tiels. They don't care that they are smaller than the bird they are bullying, but if the 'tiel has had enough the size difference gives them a slight upper hand. Just watch for any aggression, and have a ready space for the 'tiels should you need to move them out of the budgie aviary.