Amsterdam, Normandy, Paris, Colmar

See if you like this rough draft. You only may need a car for Alsace and Normandy.
If you are going to see the D-Day beaches you may want to buy a tour with a guide doing the driving and the narration.

1 Thursday, April 18 - Arrive Amsterdam Airport at 9:20 a.m.
2 Friday, April 19 – Keukenhof GardensAny
3 Saturday, April 20 – Amsterdam
4 Sunday, April 21 – Amsterdam
5 Monday, April 22 – Amsterdam
6 Tuesday, April 23 - Fly to Strasbourg (rent the car in Strasbourg or take the train to Colmar)
7 Wednesday, April 24 Colmar
8 Thursday, April 25 - Colmar
9 Friday, April 26 – Drive to Bayeux (Normandy)
10 Saturday, April 27 - Bayeux
11 Sunday, April 28 - Bayeux
12 Monday, April 29 - Normandy
13 Tuesday, April 30 Normandy
14 Wednesday, May 1 – Normandy
15 Thursday, May 2 Paris
16 Friday, May 3 Paris
17 Saturday, May 4 - Train back to Amsterdam
18 Sunday, May 5 - Amsterdam ?
Monday, May 6 Flight home

I've just been in Amsterdam, it's one of the last places I'd want to have a rental car. Only way would be if you went out of your way to pick a hotel on the outskirts, one with parking that's near a major highway. But that wouldn't make sense where one of the pleasures of visiting Amsterdam is staying in Amsterdam.

Check rental prices. There is often a huge drop-off charge for returning the car in another country. On the other hand, you will have to park the car in Paris so you'll be paying for the car rental and the parking unnecessarily. I would take public transportation to France, get a car and visit Normandy, Burgundy and Alsace in a loop and drop the car in Paris or take a linear route and then a fast train from Colmar or Strasbourg to Paris, then train from Paris to A'dam.

Trains are fast and frequent in the Netherlands and you can day trip from A'dam to The Hague, Rotterdam, Delft, Utrecht, Haarlem and more. I spent 8 days with a car in Burgundy and Alsace and would have been happy with another 8, then a couple of days in Strasbourg after returning the car.

I did something very similar, but took trains everywhere except for renting a car in Caen (after taking a train there from Paris' Gare St. Lazare) for our stay in Normandy (driving to beaches, cemetery[s], Mt. St Michel, Bayeux Tapestry!). I would never rent or use a car in a city, and find taking the train so easy and so relaxing. I think your husband is wrong, but maybe he LOVES driving.
We had 3 weeks; started and ended in Amsterdam. Took the train to the Rhine/Mosel, then to Paris, then to Normandy (renting a car in Caen), then back to and through Paris to Amsterdam. A triangle of sorts.