* That cage size is only suitable for a maximum of two small birds https://www.talkbudgies.com/housing-b...age-sizes.html
* Mixing budgies with finches is not recommended. A budgie has a much stronger beak than a finch. The two breeds have different general personalities.
* Adding a single bird to established pairs often causes problems.
Much better to house the budgie or budgie pair separately, it/they can still be in the same room and enjoy the nearby chirping of the finches.