Multisite login on two sites?

I’m running two websites on one MS install. With are practically the same, just the languages differ. Main blog is in Dutch and the sub-site is in English.

I’m using Events Manager Pro to sell city tours, but WPML kept breaking important links and settings, so I had to change to a MS install.

On my main blog (Dutch) all events are displayed. Dutch ones are created on the main blog and English tours on the subsite.

I’ve created a group of users called “Resellers”. They do not have access to the Backend Dashboard, but they can log on to the main blog and maintain their bookings on a front-end page. This works splendid. On both blogs the users are active and have the same capabilities (permissions).

But…
If a Reseller is logged in and tries to book for an English (subsite) event, they get transferred to the subsite (again, due to language differences). There he’s not logged in…

Is there a way (php coding, I guess) to have a user log on to both websites with just one login? So once they’ve logged on to the main blog they are also logged in on the subsite?

Please advice.

Thanks in advance,
Patrick.