How would you respond?

My husband and I were talking about the mail and our 5 year old came up and was trying to ask him a question (was repeating it over and over). Instead of answering or telling him to wait my husband hits him 4 or 5 times on the top of the head really fast making the last one harder than the rest. Then says for him not to talk while grown ups are talking. Naturally our son starts crying because it hurt. He starts coming to me saying daddy is mean and hurt me. My husband tells me not to comfort him and to back him up. I said our son should not interrupt adults when they're talking but I also said my husband shouldn't "hit" at all for any reason. My almost 3 year old comes up and is yelling at husband for making our 5 year old cry. Our 3 year old kicked him and said that's for hurting brother and husband turns around and spanks him on the butt and says no hitting or kicking! Then they were both crying saying daddy is mean. Then he says that mommy and daddy's conversation takes priority over there's and even I shouldn't be stopping mid-sentence to answer them or entertain them because it's disrespectful to him.