[FaeryBee]

Budgies are tiny birds and as such their respiratory systems are extremely sensitive.
When there are respiratory issues, then a drop of 100% eucalyptus essential oil used in a warm mist humidifier is excellent for helping to open the airways.

However, I would not recommend using an oil diffuser in the same room with your budgies simply for the purpose of freshening the air.
There are many other natural ways to get pleasant scents into your home.

Dried and fresh herbs and spices are great to use.
With budgie safe spices such as the ones you are using in the bathroom, you can actually place dishes of them around your apartment.
It won't hurt if the budgies decide to nibble on them and you'll have a nice fragrance instead of stale air.

You can also simmer cinnamon, nutmeg, cloves and/or allspice in a bit of water which will make your home smell amazing.

Another thing you can try is taking an orange, poking holes in it and ****ing whole cloves into the holes.
The fragrance will last a long time as the orange dries out.