Single Member LLC vs Multi Member LLC to add spouse

Hello, I have a single member LLC in bookkeeping field and I wanted to know if I  need to change my LLC to multi member to add my spouse if he also helps and works for my LLC for free?  We are both in the same field.  We file as married joint returned with the single member LLC disregarded entity.  Does it change anything with the filing?  And if I do need to add him to my LLC, how would I do that?  Do I just update the CA SOS filing and add his name?  Is there anything thing else I need to do? What are the pro and con for adding him and changing to multi member llc?  Since we are a married couple, would the tax filing for the LLC be treated the same as disregarded entity?