Hello ​@Shine 

I don’t think that you have night trains from Paris to Prague, you must change, for example travel with an ICE to Mannheim and with an Euronight from this city to Prague.

With an Eurail/Interail pass I suggest to make reservations from Paris to Mannheim on raileurope.com and from Mannheim to Prague on oebb.at.

You can also take Eurostar to Brussels (book on www.raileurope.com) and then European Sleeper to Prague (3 days/week) (book on https://www.europeansleeper.eu/en).

Also please note that there are no 4-person sleeper compartments. It's either a 4-person couchette compartment or 2 2-person sleeper compartments.