Formula to autofill neighbouring cells when a value is added to another

Try Validation.

Select the range that needs to be protected to enter only one "1" in the range.

select the range and press Alt+D+L and Settings>>Allow>>Custom>>Formula

Formula:

=COUNTIF($A2:$E2,1)=1

Give ok

Now the range A2 to E2 allow the user to input only one 1 in the range.

Change the A2:E2 to your range.