1.定语从句,这句话应该是 (我们假期住的)酒店在海边
The hotel (that we stayed during our holiday) stands by the seaside
where是副词,不跟介词at连用的
2.whom 指代 the old man's grandson is the boy 这个句子中 the boy
直译为
那个男孩,我认为是那个老人外孙(孙子)的男孩(宾语),很可爱
3.一样,我就不说了
4.needs B 应该是 need 复数名词
应该是对的,不确定,你再问问看,goodluck