You have a maximum of 2 outbound/inbound travel days. A travel day is 00.00 - 23.59 CET.
The trip you describe has 4 travel days in Germany, thus it is not possible. You can't return to Nürnberg between your visits to Paris and Brüssel.
get for the cheapiest Route of that Standardtickets or “Sparpreise” Saverfares and use Day3 and Day4 for a nice daytrip from either Paris or Brussels. (e.g. from Brussels to Brugge or Ghent) and from Paris for a daytrip to Lyon or Lille :)
You state to be RESIdent of DE-so if you hold a passpt from far away without too many stamps in it from the various stamp-happy German authorities, use that.
IF booked well advance and willing to stick to those fixed times, you could check what SSP=SuperSparpreis on DB would cost for any trip-OR for only to/fro Strasbourg for the Paris trip-or even use the 49€/Monat ticket once it is there for NahVerkehr In DE. But the wisest of course would be to not return to N and combine the 2-to save money, not time, preferably not via that Thalys. OR if money is a bit tight-check FLIXbus.