Hi Mario,
Our plugins currently don’t support tickets themselves having categories—at least, not categories that can be entered from the front-end.
I’m sorry to disappoint!
You describe this as well:
We’d like to show availability (with number of still available seats) for both categories on the event, so once the given category is sold out, the availability turns to red color and “sold out” appears.
Our plugins do currently provide this for tickets generally—if you specify the stock for an RSVP ticket, for example, as 100, and 100 people make RSVPS, then it will say, “Sold Out” and folks won’t be able to buy make more RSVPs.
Please let me know if there are any other issues or questions I can try to help with.
Thanks,
George