If you make reservations at the national railway companies you can, at least for Sweden, choose your seat.

Here is a guide on how to make make reservations:

Thanks AnnaB for the reply. I should have perhaps been more clear - it is the Eurail Seat reservation process I was querying

I’m aware of individual train companies where you can  - those that are relevant to how I will use the Pass next month, such as OBB and DB

If, on Eurail I’m just going to be allocated a seat that can’t be chosen or changed on say TGV Lyria, then it may impact one of my journeys home. To pay €37 extra for a seat on the lower deck with limited window, may change my journey

It depends per country and sometimes even per traintype. IF it is not possible before, it may-sometimes- be doable by calling the centre of the railway concerned. There is NO unified system, whatever snazzy USAer may find or think. The joys of travel_ 33 different countries each with their own habits.

It is also quite easy to at least lower the high expense for a direct train overtheborder by cross border on local train and use TGV only INside FRance.

It's not possible to choose your seats when using our reservation self-service tool. These are automatically assigned. In practice, you might be able to switch to a different preferable seat once you're on the train as long as it has not been reserved by another passenger. 

This is completely crazy. I am travelling with my partner and 2 kids and we all got split up on different seats. We should be able to select our seats together. The kids don’t even have a window. We reserved these seats about 8 months ago so there is no way the train was already so booked up that these were the only seats available. There has to be a way to deselect seats like on a plane. It’s just not safe, especially with kids. We have just sat together for now and will please with people who have booked these seats to swap with us but this is a ridiculous system. My friend booked tickets not using eurail and was able select where they wanted to sit easily and they only booked 6 weeks ago. There simply must be a way to ensure our extra cost reservations are seated together. 

8 months ago ? It is not possible to book a train so long in advance, except Eurostar but then not for passholders.

Where did you book the reservations ? Going through eurail.com it is indeed not possible to choose seats but by going through the railway company it often is (you also avoid fees).

Also be aware that seat numbers generally aren't continuous, like 22, 23, 26, 27 for a bay of 4.

If you have further trains on your trip I'll gladly help.

Ah that’s right…we bought the eurail 8 months ago and reserved the seats as soon as we could…can’t even remember when that was but it was ages ago. It’s a flawed system if through the eurail reservations process you get randomly seated throughout the carriage without being able to change it. I would tell people not to use eurail because honestly, the small savings you gain are not worth it for all of the issues with it. Having to print out the reservation is ridiculous when we have a mobile pass. So many quirks and functionality restrictions that seem to have been around for years but never sorted out. 

If you make a reservations for 4 persons together, you will be seated together if there are seats together available when you make your reservation. 

The recommendation from the experienced travellers in the community is to only make reservations through the Eurail website if no other options are available. Please read more about that below. 

Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days. 

 Planning

The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries. 

 Reservations