The system doesn't recognize his or my ID numbers when we try to add each other and forces us to create a duplicate record.
@Annie Thompson For privacy reasons the system is set up so living individuals cannot be searched for and found. If you are wanting to see his ancestors on your account you will need to create duplicate records for the living ancestors to then link to the deceased on his pedigree.
Short Answer: That is because you are both "Living".
Let me explain ...
Bear with me ... I am very 'verbose' ... that is my 'style'
We CANNOT 'see' or 'use' the "FamilySearch Person Identifier" (PID) of ANOTHER ("Living") User/Patron in our own (respective) 'FamilySearch' Account.
You BOTH have to CREATE a NEW ("Living") individual/person (and, 'Yes', a "Duplicate") of each other in you respective 'FamilySearch' Accounts.
And, you BOTH have to do the SAME of ALL the "Living" individuals/persons in your COMBINED "Ancestral" lines.
Basically, you have to "Build" a "Bridge", between you, of ALL the "Living" individuals/persons that connect/link you together.
Most NEW Users/Patrons DO NOT understand the BASIC concept/model and premise of "Family Tree" of 'FamilySearch' ...
For starters ...
We do not have our OWN "Tree" in "Family Tree" of 'FamilySearch'.
We ONLY have "Branches" (ie. Ancestral" lines), that are interconnected, in this SINGLE "One" World "Tree", for all of us, that is "Family Tree" of 'FamilySearch'.
"Family Tree" of 'FamilySearch' is NOT like 'On-Line' "Websites" (eg. "Ancestry_com"; or "MyHeritage_com"; or, the like); and/or, 'standalone' personal (computer) programmes (eg, the OLD, now no longer supported, "PAF"; or, "Ancestral Quest"; or, the like).
We DO NOT have "Private"/"Personal" 'Trees' in "Family Tree" of 'FamilySearch' like other 'On-Line' "Websites"; and/or, 'standalone' personal (computer) programmes.
We do not even, own; or, manage; and, are NOT even responsible for, the "Deceased" individuals/persons in "Family Tree" of 'FamilySearch'.
"Family Tree" of 'FamilySearch' is built on a "Open Edit" Platform - hence, why any registered User/Patron can "Edit" (ie. Add, Delete; and/or, Change) ANY "Deceased" individual/person in "Family Tree" of 'FamilySearch'.
You can certainly 'see' and "Merge"/"Combine" any "Deceased" individual/person in "Family Tree" of 'FamilySearch' with another "Deceased" individual/person in "Family Tree" of 'FamilySearch', regardless of who the User/Patron was that initially created those "Deceased" individuals/persons; as, they DO NOT reside with the User/Patron who initially created them - they are "Public".
If fact, you can ONLY see "Deceased" individuals/persons in "Family Tree" of 'FamilySearch'; except, with this 'rider', that you can ALSO only see "Living" individual/person in "Family Tree" of 'FamilySearch' that YOU created; as, they reside in your "Private Spaces".
No other User/Patron can see ANY "Living" individuals/persons that were created by another User/Patron; as, they ONLY reside in the "Private Spaces" of the User/Patron who created them.
We CANNOT even see the ACTUAL Record in "Family Tree" of 'FamilySearch' of our IMMEDIATE Family (eg. Spouse; Children; Parents; Siblings; ETC; Etc; etc) if they are "Living"; and, they have their own 'FamilySearch' Account.
Of course, you can create your "Living" Family members; and, record them in "Family Tree" of 'FamilySearch'; but, they will ONLY be seen by you:
▬ You cannot "Share" them with any other User/Patron.
▬ You cannot "Merge"/'Combine" them with any other "Living" individual/person residing in the "Private Spaces" of another User//Patron.
There is CURRENTLY no mechanism in "Family Tree" of 'FamilySearch' for Users/Patrons, to "Share"; or, "give permission" to "Share", the "Living" individuals/persons in their own "Private Spaces" with/between other/another User(s)/Patron(s).
There are a myriad of "Privacy" Laws within the many various Countries and Unions throughout the World - it is a nightmare to negotiate.
"Family Tree" of 'FamilySearch' is used in many Countries and Unions throughout the World; and, as such, must adhere to the myriad of "Privacy" Laws throughout the World.
Hence, "Privacy" is one of the reasons that we cannot "Share" the "Living" individuals/persons in our own "Private Spaces" - it is NOT the ONLY reason; but, certainly has a bearing on the matter.
Another factor is that such would have to be 'Coded'/'Programmed' into the Programme that is "Family Tree" of 'FamilySearch'.
'Yes', these "Living" individuals/person in "Family Tree" of 'FamilySearch' WILL, in fact, in many (most) cases will be "Duplicated" - unfortunately a necessary situation that currently cannot be avoided.
I know that there are "Duplicates" of the "Living" ME - at least, one for my Wife and each of our Children, not to mention my other ("Living") extended Family members.
Here are some "Knowledge Articles" in 'FamilySearch' in regard to "Private Spaces" and "Living" individuals/persons:
What is a private space in Family Tree?
Who can see my living relatives in Family Tree?
Here is a good place to start, with how things work in "Family Tree" of 'FamilySearch' (and, other programmes as well):
Introducing The Family History Guide
The Family History Guide
I hope this helps.
IF, you have any further 'Questions'; THEN, do not hesitate to ask.