Should be possible in the next few days :) 

Usually train opens for Reservations 90 or 60days in advance for Poland just 30days in advance. 

If you let us know which Routes you are looking for we may can suggest the Website of the original operating Company :) 

Thank you!! Our trip plan is:

• Dec. 14th, Geneve - Bern - Interlaken - Geneve
• Dec. 15th, Geneve - Dijon
• Dec. 16th Dijon - Strasbourg - Dijon
• Dec. 17th Dijon - Chamonix
• Dec. 21st Chamonix - Zermatt
• Dec. 23rd Zermatt - Chur (on Glacier Express) - Luzern
• Dec. 27th Amsterdam - Bruges - Amsterdam

No reservations are needed for domestic travel in Switzerland. For Genève - Dijon and Dijon - Chamonix, you'll need reservations for TGV or IC trains in France. But you can also travel entirely with reservation-free TER trains.
For Amsterdam - Bruges, you need a reservation if you use Thalys but you can travel reservation-free every hour with an IC train. Better still, forget Bruges and go to Antwerp or Gent, which are much less of a tourist trap…

Luzern - Amsterdam seems to be missing but you can book (optional) reservations via the DB website.

Thank you so much. What about the Glacier Express?

If you really want to ride that train, you will have to make a reservation indeed: https://shop.glacierexpress.ch/gex_en

But there is also an hourly, reservation-free service on the entire route. You will just need to change trains a few times.

@Marvin Carvajal  Here my post about the regional trains on the Route of Glacier and Bernina Express :)