Is it permissible for a husband to stop his wife from visiting her family?
A husband shouldn`t stop his wife from visiting her family, and it is disliked for him to do so because such an act makes them harbor feelings of hatred against him.
I am an employee at Social Security, and I have heard that working with them is forbidden (haram) because they impose an interest rate of 2% on companies and individuals who are late in making payments. Is my job with them haram or questionable?
Please clarify the type of work. If it does not involve the usury (Riba) mentioned, we hope that there is no issue with it, as most of their funds are acquired in a lawful (Complies with the teachings of Sharia) manner. And Allah, The Almighty, Knows Best.
Is permissible to buy/sell with non-Muslim?
Yes buying/selling for a Muslim with non-Muslim is permissible as regards what is lawful.
What should a person, who doubts the validity of his Wudu, or over performs it, do?
One who doubts the validity of his/her Wudu while performing it should redo it until he/she is certain of having attained purity. But, if doubt was after having performed Wudu, then he/she should not pay attention to that as doubt after the end of an act of worship does not count. This is of course in case doubt was within the reasonable limits since once it goes beyond that, it becomes a whispering of the Shaytaan (devil) which he/she should ignore as the Wudu is valid.