Ответ:
1)This is the coffee bar where my friends have a drink.
2)You can buy everything what we saw in a shop yesterday.
3)Old people in my country, many of whome are widows and widowers, often move to an Old People's home.
4)I can't hear anything that/what you are saying.
5)I'd like you to meet my brother with whom you will be studying next year.