Skipping over what others have pointed out - you don't interview a co-founder.
a) ensure this is someone you are going to get along with
b) get someone else to assess their technical competence - you can't assess it and the guidelines you provide won't work reliably.
a) ensure this is someone you are going to get along with b) get someone else to assess their technical competence - you can't assess it and the guidelines you provide won't work reliably.