While this wiki will not address why the film is different from the cartoon....I will give my theories here! So let the cloud rain....
Where are the Maitland Couple?
In the neitherworld more than likely. After finding peace with the Deetz family, they then were upgraded and placed somewhere in the neitherworld. The rules may change in a peaceful situation.
Why is Beetlejuice Around?
He may have been granted a second chance by Juno after Unknowingly getting the Handbook for the recently Deceased out of Otho's hands. His Anti-hero moment. He was most likely assigned a mission to maintain the balance of things as Lydia knows a great deal about the afterlife already, therefore to deal with it. Beetlejuice may have in the meantime developed this slightly more healthy relationship with Lydia, viewing them both as outsiders in they worlds, therefore finding common ground to start from anew.
Where is Juno?
Her time was up, it would appear, her working with the agency for the recently deceased had special perks as far as how it ends. The argument of how long ago her death was, maybe part of the perk. Sort of like, If you work here you stay around longer. We know Beetlejuice was a old timer too.
How old is Lydia again?
14 during the animated run. Therefore she was younger during the film. Is it that hard to believe she was 13 or 12? She acted older than her age as stated by Barbara Maitland.
Are Lydia and Beetlejuice a Item?
I would say during the cartoon run, they were dating but doing things the right way. Sometimes it felt like Beetlejuice was being maintained by Lydia which also may have been planned by Juno. Either way, Lydia and Beetlejuice were developing a friendship too, so it may have been a way to do things right.
Wormland.....I thought that the moon near Saturn housed those worms?
Most likely this is a area where in the other world (real world) the saturn moon was where they are. But the neitherworld is different. Also, the recently dead don't have the same rules about them as normal neitherworld ghosts.
There is a start to my theories. What you'll think?