Tickets for attractions in London

Will be in London next week, during the week, for two days, along with my family (3 children, 2 adults) for a city trip, through Eurostar.

Initially thought a day-pass on Tube for each day would be enough but found
boat trip is cheaper during Jan/Feb/March, 50% off for River Red Rover all day sightseeing.

I just need to go from St.Pancras to take the boat and may need to come back in the evening to St.Pancras to my hotel.

-Would I be able to cover many attractions on unlimited Boat trip for a day?
Do I still need a day pass for the tube for the first day, to take a boat from London Eye /WestMinister or Tower (and back to St.Pancras)?

-As I don't seem to find any cheaper combi-tickets, what is the cheapest way to see following attractions (not sure which one I need tickets for yet)? Book ticket online for each place in advance or queue up and buy onsite?

[Tickets]??:
* London Dungeon.
* SEA LIFE London
* London Eye (closed for maintenance), instead do The view from the shard?
* Madame Tussauds

[no tickets]??:
* Westminster Abbey
* Buckingham Palace to see the Changing of the Guard.(second day)
* Trafalgar Square
* St. Paul’s Cathedral
* Monument to the Great Fire of London
* Tower of London
* Docklands
* Canary Wharf
* Greenwich
* Big Ben
* Tower Bridge