Linking account to new Game Center

Hi there, I have an issue..... My son and I both have a COC account at th9. He started his on my old iPad v1 and I have a newer iPad. We didn't realise until too late that they were both on the same Game Center account. When we logged in the lower of the 2 would always be asked to upgrade to higher but we always just said no and we are able to play our own accounts. We have purchased my son a new iPad and can't seem to transfer the lower account to this. We have now logged into a new Game Center account on the old iPad and it welcomes him as his new Game Center account and still opens the th9 but looking in Game Center on the old iPad it doesn't have any of the achievements etc. when logging into the new iPad with the new Game Center account it starts from new and hasn't linked. We are launching from within Game Center which was what supercell suggests. Is there a way to link to a new game center account on ipad1? Thanks in advance.