Given a proton nmr, How do i estimate the amounts of isomers?

The area under each peak (the integrations) depends on the amount of compound present and the # of protons that it represents. If you've got two isomers, then comparing the integrations for a 1 proton signal from each isomer will give you the relative composition. (Works for 3 or more isomers too, but at that point it gets increasingly difficult to identify which peak is from which isomer.)