Using time capsule to restore data to new computer and doing the back-up for the new computer

Hello

My iMac has broken down. Data were saved by Time Machine on a Time Capsule. So the new computer was set-up with things from the Time Capsule. Worked fine. The Time Machine informed me that the backups will no longer be available for the old iMac. That's fine. After everything was set-up on the new one (15" Mac Book pro retina) I wanted to make sure that the backup process for this one was ready to go and as it was done in the past. I have selected the Time Capsule (it's a 500GB that is backing two computers) and as such there is limited space available on it but that's ok since the process is creating space when needed by deleting old backups from 2011 which I don't need any more keeping 1 year history being ok.

The problem I am now facing is that it seems Time Machine consider that the back-up of the New Mac book pro as a new volume - i.e. on top of the one used to set-up the new Mac book (the old iMAc!) and the one for the other computer. Time machine seems to be looking to open a third volume and obviuosly doesn't have the space to perform the back-up.

How can I sort this? Ideally for me after I have restored the data from the old iMac to the Mac Book pro I would like to keep updating the back-ups (originally from the old iMac) with the changes that happened on the Mac Book pro.

I hope I am clear and looking for some tips on that.

Many thanks in advance.

Best

Pierre