iphones sharing the same id

I have 2 iphones which share the same appleid . One is essentially a clone of the other . This has worked successfully for some time but on a reset caused by one of the phones shutting down , the 2 phones have been linked together somehow . Both ring when someone calls one of the numbers ( but not the other way round ) and both get the same texts sent to either one

Reading some of the blogs , it seems that the only way to 'unlink' them is to create a separate id for each phone and let them live their own lives ; but we only have one email address and dont really want to set up another one

Help