Grundschule in Berlin

Hi,
We are moving to Berlin next summer. We have 3 children, two of whom we will need to find schools for. The eldest will be 7.5 and the second 5.5. They've both been at a Montessori Primary school and we like that method but the main thing for us, is for them to be immersed in the German language. They are bilingual english/Swiss German and understand a little high German but would need a lot of help at school.
I've been going around in circles trying to find a school for them. I know we have missed the application dates (if anyone can advise me about that, I'd be grateful!) and that the second will be too young for the school system (but we do need to find something other than kindergarten for her...) A bilingual school would be fine, as long as there really is a lot of German taught.
We don't know where we will be living yet. I was trying to find a good school first...!
If anyone has any suggestions, I would really appreciate it!
Thanks very much in advance!