> they are a newish small company and i dont know how good they are at keeping books etc and having 'events that trigger payment'.
An example of an "event" for them would be "received some income from film x". This should trigger "check if person a, b or c need paying".
If they can't do that, then they shouldn't really have contracts that are paid on that basis. I would think they could do it.
Even if they can do it, in your place I'd be calling regularly to see if I'm owed more money and whether I should be invoicing more.