Eurail is for non-European residents.

Interrail is for European residents.

The main difference between the 2 is that Interrail can only be used for 2 days in the country of residence, Eurail has no such rule.

The Primary ID document expected to be used as proof of residence is a passport.

Anyone can use the Global Pass but keep in mind that you can only travel on two days in the country of residence you select when booking (and need ID as your proof).

With that in mind, what valid passports will you both have with you at the time you plan to travel? Assuming you might have dual citizenship.

Paper Passes can be delivered to most of the UK, yes. You can also get a mobile Pass (a digital version that's an app on your phone). All that info on the Eurail/Interrail websites.

Hi @Al_G and @JDH thanks for the info.

My questions goes on the lines of what you are both mentioning. Living in the UK for now and with brexit and such I don’t really know what the details are with that. 

as @JDH mentions, I do have dual citizenship. I will be traveling with a Spanish passport for visa purposes, but will have the mexican as well. 

My issue comes with them asking for proof of residency and well this trip is a farewell to Europe for the time being and we will leave our flat from the UK.

This is where my confusion goes. Also, seeing as a European I can’t travel within my country for more than 2 days with the interrail pass I don’t plan on traveling in spain.

Any advice?

Brexit is irrelevant for Interrail and Eurail.

Firstly there is no phone number to contact Interrail/Eurail. Most of your questions are answered by the FAQs on the website, but here is are a few answers.

People with a permanent country of residence should declare that in their purchase. 

If you have proof of any residence in a European country ( e,g, a residency permit or visa) including the UK you should get an Interrail Global or single country pass. If you only have temporary residence you should use your citizenship or permanent country of residence for choosing your pass.

If you have proof of residency or citizenship outside Europe you should get a Eurail pass.

The only difference between a Eurail or an Interrail pass is the basic rule that with an Interrail Global Pass you can only use the pass in your COR for a maximum of 2 days.

If you choose a mobile pass it will be delivered electronically to your e-mail. Paper passes can either be acquired at main stations or posted to any address convenient to you. You do though need to allow a good period for delivery (several weeks)

As @Yorkie says, better to both use your Mexican passports as your ID (for your Eurail Passes, regardless of what other ID you're using for other stuff). Select Mexico as your country of residence when booking the Passes. That'll make the travel you want to do in and out of the UK much more straightforward And passport is also simpler proof of ID than anything else too.

Thanks @Yorkie @rvdborgt and @JDH  

i guess using this passport to travel is much better. Question though, I will be entering Europe from the UK with the Spanish passport as we will be traveling upwards of 90 days and for visa or permit issues this is much better. 
 

doy you know of this can be an issue in case I move around with a Mexican passport? 
i know I’ll have to carry both. 
 

sorry for all these questions, I’m new at dealing with dual citizenships and not living any… (fyi living in the UK under student graduate visa with mexican pssport)

The passport you use for Eurail is totally separate from the passport you use for other things, such as passport checks at the border. It doesn't have to be the same.

Everyone is amazing!!! 
I can’t thank you enough! 

this seems to be an amazing community glad to join!!