Why are you bringing them onboard as a co-founder and not employee? I don’t know what’s your arrangement with them for salary, if possible - get them started as

Why are you bringing them onboard as a co-founder and not employee? I don’t know what’s your arrangement with them for salary, if possible - get them started as an employee, once they have proved their mettle, then you can promote them to co-founder. If you are able to see traction then depending upon how much funds your company has at that time - either you can take out your investment or get equivalent in equity. Hope it helps.