Salam 3alaykom,
My friend has a married sister and her husband is not in a good financial status, she said she wanna give herf rom the zakah money, I told her, he has a shop and a car and he owns a house, she said but at the end of the month it really narrows down on money and he has 2 kids. How can we tell if someone is in need of zakah? because the imam in the masjid told me if you pay the zakah and later on you knew that the person you gave was not in need of that zakah then you have to repeat the zakah on someone in need of it else, it wont be concidered as zakah.
Clarify the situation may ALLAH grant you good health.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The fact that a person owns a house, a car and a shop does not necessarily mean that he is not among the people who are eligible for Zakah. It might be that his earnings are not enough for his basic needs, and he should not be asked to sell the house, car and shop because these are basic things which are indispensible for him. A poor person (Faqeer) who should be given Zakah money is a person who does not have his sufficient needs or that he only has less than half of his sufficient needs, and a needy person (Miskeen), is the one who has more than half of his sufficient needs or most of his sufficient needs. What we mean by having sufficient needs is having one’s own needs and the needs of the people whom one is obliged to spend on: each one of them should be given what fulfils his sufficient needs within reasonable limits. Therefore, if the person whom you mentioned in the question is so, and he has not his sufficient needs and his need is not a result of being extravagant, then he should be given from the Zakah up to suffice his needs. Moreover, it is permissible for your colleague to give her Zakah money to her sister if the situation is as we mentioned.

For more benefit on the permissibility of giving Zakah money to a sister, please refer to Fataawa 84467 and 84916, and to Fatwa 88368 on giving Zakah to whoever one thinks to be a poor person and then it transpires that he is rich.

Allaah Knows best.