Rarely. There is a condition called a paradoxical embolism in which a leg vein blood clot can dislodge from the leg, float up into the hear, & then travel through an abnormal hole in the heart called a patent foramen ovale, then float up into the brain causing a storke. Since you need both a congential defect in the heart, a DVT, and a embolism of the DVT for this to occur, it is possible but not common.
Yes possible. Either you can have hypercoag unable status which means u form clots more than usual or in some patients with a condition called pfo/ patent foramen ovale where right and left heart chambers/ the atriums can connect directly and clots from leg can travel through veins from right to left side of heart and can cause a stroke in a condition called paradoxical embolism.
Yes. A blood clot in the leg is typically in a vein and if it dislodges it may go to the heart. Most of the time it will pass through the heart and go to the lung. This is known as a pulmonary embolus. In some people it may pass through one side of the heart to the other and then go into the arterial blood system, even to the brain where it may cause a stroke.