英语语法 "in"

第一句,in是副词,可译成在家,与outside 相对,your father是主语,is 是系动词,in作表语
第二句,in 是介词,in 的逻辑宾语是coffee I是主语,don't like是谓语,coffee是宾语,with milk in是coffee的定语,由于在句中有in有逻辑宾语coffee,故in不能省略

Is your father in? in 是 副词词 作表语

I don't like coffee with milk in. in 介词 with milk in整个做定语