tower of london is roughly 8-10 stops on the district line. If you have a travel card will cost you no extra. probably take you about 20 mins

London eye is near waterloo you can go to westminster on districe then join the jubilee going south for one stop i think.

madame tussauds is outside baker street, you can get victoria line up to euston i think lol without looking at map then get circle metropolitan or hammersmith and city going west to baker street

Its all from rough memory so someone might show me wrong but i think im right.