Substitutions at 4' and 6' positions of 3-chloro toluene are not normally possible because carbocations are prone to rearrangement.
Hexane is a 6 carbon chain. starting at one end, number the carbons 1 - 6. 2-methyl 3-chloro means that the methyl group attaches to carbon 2, and the chlorine attaches to carbon 3. 3-methyl 2-chloro would simply be the other way around. They are two unique and different compounds.