I realised rail Europe was a bit of a rip off , but the sncf site does link to it
I remember having heard that Rail Europe is a subsidiary company of SNCF, that might explain the link.
See [www.voyages-sncf.com] for the Paris-Brussels route; btw, Thalys is the only direct train service on this route, the only alternative would be to take regional trains, which involve several changes - see [www.bahn.co.uk] and tick "local transport"; add IR trains, otherwise you'll get an estimated travel time that's slower than walking.
For Brussels-Amsterdam, [www.b-rail.be] is the website you need to check prices.
considering there is an 90 minutes between each leg of the tour
Brussels-Amsterdam on Thalys is more like 2 hours, by Intercity train its even a bit longer; still faster than going by bus, though.
The most user-friendly website for looking up websites throughout Europe is the one of German Railways that I mentioned above - www.bahn.co.uk. Although in many cases it does not give you fares for travel outside Germany, which means you will inevitably end up on the national railway sites again.
If rail travel is too expensive for you, you could consider [www.eurolines.com].