You don't at all need nor want a car in either city. And w/ only 7.5 days 'on the ground' you really don't have time to tour the countrysides.

I'd book open jaw into one city and home from the other - otherwise you wast a day backtracking to fly home.

I wouldn't divide the time exactly in half - I'd do an extra day in whichever city is at the front end. Both because arrival/logistics eat up about 1/2 a day, and because you'll probably be jetlagged.

There is absolutely no need for guided coach tours - however there are good 2-ish hour walking tours in both cities.

As for what to see/do-there are literally hundreds of options so start by checking general guidebook(s) and clicking 'Destinations' above and read upa bit.

Tell us what sorts of things interest you. Also - which hotel chain(s) are you using? Most have multiple properties and there can be huge differences in the locations.

A car is not only not necessary in cities but it is a handicap since you'll waste valuable time looking for parking and getting lost on one-way streets. You may walk blocks from your parking place to your destination so forget the car.

If you're thinking of any day trips out of the city I would only visit 1 location - either London or Paris - not both. You don't have enough time to do justice to 2 cities, travel between the cities, and take a day away from either to travel out of town.

Both Paris and London are diverse cities offering many many choices of sightseeing. Some idea of your interests would be helpful otherwise you'll get a list of other people's favorite places.

Check guide books or click on "destinations" above to get an idea of the basic tourist sights. Put together a tentative itinerary and come back for advice.

Pick up some guidebooks. The Michelin Guide for Paris might even have a 4 or 5 day itinerary suggestion.

We celebrated our 20th in Europe with our kids--and since the 20th is the "china" anniversary, bought a set of Villeroy and Boch. Think of some nice chatchke for a memento.