Apply a number to differentiate cells with same value

Hello,
Can someone help me please? Here is my issue.
So I have a long list of memberships. The issue I have is that I have one primary member that has a spouse and 2 kids and each one needs a unique number based off the primary member.
Example: Member 1000 is John Smith and
his wife would be 1000S for spouse and
the kids would be 1000C.
The issue I have is that there are two kids and I need to assign a 1 to one and a 2 to the other to have the numbers be 1000C1 and 1000C2. In some cases there is more than 2 kids. There is too many memberships with this situation to do it by hand. Is there a formula that can do this?

Thank you for all your help.