were having是过去进行时,表示过去某个时间正在做什么,如：we were having a meeting when the boss came in
are having是现在进行时,表示说话时正在做的事,如：we are having breakfast
will have是将来时,表示将来将发生的事情,如：we will have a meeting tomorrow morning
have是一般现在时,表示事物的常态,如：we have English class every day