trip to amsterdam(holland) belgium and paris in spring

Fly into Paris, out of Amsterdam as an open jaw flight (not two one-way flights) or vice versa.

Get between places by train. Try one of the train websites like SNCF or the Dutch NS website:

https://en.voyages-sncf.com/en/train-ticket
https://www.nsinternational.nl/en

or also a third party site that is well-regarded: www.trainline.eu .

What not to miss? This is where a guidebook is essential. Rick Steves has good guidebooks covering all of these places. There are also lots of things on his website (sample itineraries). You should also look at other people's trip reports and read what they liked and didn't. However, all of these places are pretty easy to explore on your own even without knowing any language but English.

As always, www.seat61.com is your best guide to rail travel between cities. To understand cities, start with the Explore Europe section of this website, which already provides a great deal of information.

which of the three months of Spring do you mean?

Advance-bought tickets give you tremendous discount. From Amsterdam to Brugge can be as cheap as some EUR 35 in 2nd class.
It pays to compare the various companies. They differ considerately in ticket prices for exactly the same train. In addition to the above-mentioned, there is also the Belgian national railways: www.b-europe.com.

We stayed in Brugges a couple months ago. Stayed at Hotel Ter Brughe. It was wonderful. We had a huge beautiful room with a canal view. On the lobby floor so no stairs. Saw swans swimming in the canal right outside our window one night. It was magical. Great breakfast too. Enjoy. Brugges is a wonderful town.

Also, was in Paris a couple of years ago for 5 nights and used vacationinparis.com to book an apartment. Very reasonable cost and loved staying in an apartment instead of hotel. Felt like we lived there. Loved, loved, loved Paris. It was very easy to get around. If time allows, be sure to train to Versailles for the day.

Need to be careful about apartments in Paris these days. The city is cracking down on unlicensed rentals.

Paris- Hotel Relais Bosquet

Amsterdam- Hotel Vondel (museum district) easy express bus service to and from airport. 10 minute tram to Centraal station.

Train is a great way to get about. Make sure you can each handle you own luggage.

Take day tours if there is one that interests you.

Reserve Anne Frank house tickets n advance.

Thanks for your help . We are planning to go in April and I will look into sites you suggested

So if there in April, do you have Keukenhof https://keukenhof.nl/en/ on your list?