1. Should my grandpa be stay in the hospital?

我外公需要住院吗？

还能这样说：

Does my grandpa have to be in hospital?

Does my grandpa need to be hospitalized?

应用解析：

stay ahead (of) 领先，（走在……的）前面；

stay at 暂住在…… 投宿在……

stay away (from) 不在，外出；走开，别接近；

stay behind 留下来不走；留在后面

2. I am checking into the hospital tomorrow.

我明天要去住院。

还能这样说：

I need to be hospitalized tomorrow.

Tomorrow I need to go into hospital.

应用解析：

check at 对……发火；

check in 签到；报到；办理住宿手续；归还所借书籍；

check (up) on 调查，核对，检查；

check with 与……相符合；与……协商

3. You must be hospitalized at once.

你必须立即住院。

还能这样说：

You should go to hospital without delay.

You had o stay in the hospital immediately.

应用解析：

for this once = just for once 就这一次；破例一回；

if once = when once 一旦；

more than once 不止一次，多次；

not once 一次也不；

once again 再一次

4. Do I have to stay in the hospital for long?

我必须住院很久吗？

还能这样说：

Do I must have a long stay in hospital?

Do I have to stay in hospital for a long time?

应用解析：

stay the course 持续到底，坚持到底；

stay by 待在……的旁边，留在……旁边；

stay out of 不参与；不插手；置身于……之外