It was the same problem back in the day, with Holden Panel Vans .but as the the rods were exposed, I just pulled both to the center to open. In your case, I think they are enclosed, and would be a bit of a bother to adapt.
My 1993 Hiace camper van doesnt have a handle to open rear door from inside. Does anyone else have the same and does anyone no how to fit one
Hi
Back in a previous life I had a couple of Hiace campers. Some had an inside handle some not, depending on whether it was a van on a minibus originally. I forget the details now but i did modify at least one by fitting a stiff pull rod/wire at the window sill level that went down inside to a lever on the central lock below inside. Most car type door locks are operated by a pull rod from the remote door handle.
If you go to the wreckers and look at some doors you will probably find the correct parts to fit and only have to drill a hole or two to fit them.