pansonic kx tg5571 expandable phone

not sure if this is correct topic. if hot, send me in right direction.
bought and expandable system (pansonic kx tg5571)with 3 handsets. first add'l handset registered as #2 but then remaining 2 registered as 5 and 6.
tried to unreg and rereg it but same results. not a major deal but ease of operation and helping my kids to remember which phone goes where i'd rather have them as 3 and 4. is this possible?
thanks