Everyone on a PNR has to be in matching booking classes AIUI - this is not something a 'real person' can override/change or that the online engines take an 'easy way out' on. So you'd still be faced with either one PNR in a higher bucket or two in different buckets (the biggest problem I can think of with two PNRs is seating request/entitlement unless you're Gold and can get the TCP done).