Anyone took accommodation invitation letter fir your dependent visa from a family friend? If yes, what documents you submitted

My husband is on Skilled Worker Visa and I have to apply for dependent visa from outside UK. My father's friend lives in UK and willing to give the invitation letter citing for both of us to stay given they have enough room as per UK accommodation laws. What other documents do I need to get from them other than invitation letter given they have their own house.

Thanks in advance!