There is no specific narration that prohibits marriage between relatives. However, it might be recommended to avoid marriages among close relations in more than one generation.
It is not sufficient to prostrate on the agate based on an obligatory precaution. When one loses the prostration clay (the turbah) during the prayer, one can cut the prayer, look for something else to be prostrated upon and repeat the prayer.
The taharah is not established by this; therefore, when you wipe the najis part of your floor with the mop, it becomes najis every time you do that, and the najasah is spread to surrounding areas. One should pour the water on the najis part of the floor, and then collect the water with a cloth or mop, and the place will become tahir.
