Traveling only within Benelux, BUT flying to and from Duesseldorf from USA

We are flying in to Duesseldorf, then going by train to Maastricht, from there to Bruge then to Amsterdam and from there back to Duesseldorf to fly back to USA.
We will take some short day trips by train within Benelux also, but the major distances/destinations are as noted above. There are 2 adults over age 60 in our party.

Does it make sense for us to buy passes and, if so, what type and for how many days. We will definitely have to travel by train at least 4 separate days in order to reach our destinations, as noted above, on different days (within 3 weeks time).

Thanks in advance for your assistance!
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