Staying longer in another Schengen country other than visa issuing country as EU family member

Hi all,

I live in Ireland with my EU husband and got a Schengen visa type C Multi entry to travel to his EU home country ( Spain) to visit . I used to reside in a Schengen country before so I’ve also visited many Schengen countries with him.
We are planning to stay 5/6 days in his home country and thinking of possibly going to another Schengen country for 12/13 days and come back to Ireland. I have heard that staying longer in another Schengen country that is not the visa issuing country can get problematic. Does it also apply to EU family member who is traveling with the EU spouse or it’s just for tourists?

This will be my last Schengen visa as I will not need a visa to travel to Schengen countries as I will have my EU family member residence card soon. Please let me know if that’s allowed as I’d like to be as compliant as possible. Thank you 🙏