From your description it's clear that Tweet was a very much loved budgie in his previous home, since he is a talker and is so well socialized with people.
These trips to the Kindergarten and the change of scenery is likely adding stress on your budgie and it would be best to keep him at home and in the familiar room Oliver Tweet is used to. You can also use this very room to spend quality time with him. Since you have cats in your household, this would be the best way to proceed in order to avoid an accident.
While it's great that your Oliver is already so closely bonded to you, it's important for him to be able to entertain himself while on the cage and to eat when you're not around. You can work with Oliver in terms of helping him to be more independent. Clipping wings will not solve any issues, it will only render Oliver unable to fly and be even more vulnerable.
When a budgie is so human oriented and closely bonded to us, the chances of this bond to suffer a drastic change is slim when introducing other budgies.
The budgie's overall happiness and well being should always come first even if changes in dynamics are bound to happen.
Later on when you find most suitable, you can slowly introduce Oliver to your budgies by placing the cages close by in the same room and see how they will react. Oliver may even be able to help your budgies to be more trusting of you and as a result the bond with them will also improve.
Many times I have used the special bond I had/have with a budgie to help tame other budgies.
RIP sweet Tito (Summer 2008 - January 17th 2013).
You are missed and never will be forgotten.
Last edited by aluz; 03-21-2016 at 08:29 AM.