Hi Riyaj,
Take a help of your ABAP'er. The procedure may be like this.
1)Create a Z-table where you can maintain USER ID AND ORDER for ex:
USER ID ORDER
-------------- --------------------
USER-A INCREASING
USER-B DECREASING.
When USER-A logs into system and try to change the order, select the ORDER for USER-A(as it is only INCREASING), Check the current order and capture the new order which he has entered.
IF NEW_ORDER > EXISTING ORDER.
show error message.
ELSE.
continue with your requirement to proceed further.
ENDIF.
Hope this will resolve your issue.
Thanks
KH