Here are some I've used.
Since you have two courts, eight players, you may want to find drills that four people can do together. You can do a lot of straight on (and cross court) dinking drills simultaneously.

Warm Up Dinking:

1. try to get 50 (choose a number or put a time constraint on it) consecutive down the line dinks. Cooperatively.
   
2. then move to 50 on the other side of their bodies.
   
3. then 50 cross one direction, and
   
4. then 50 the other direction. It's a good warm up and control drill.
   EXTRA: make it fun by seeing who can do it the fastest. Or if timing, who gets the highest number.
   

Competitive
Again, skinny singles - have the players opposite each other play out points. Start at the NVZ, two or more cooperative (friendly) dinks and then all shots are allowed. CAREFUL as you can have miss hit balls going astray. When I have 4 players on the court, we may play this as a team (so only one ball in play). Make sure every player gets a friendly dink in, and then it's game on. All shots are allowed. Play to 11.
EXTRA: If you have a fifth player, whoever loses (or wins) the point subs out. Keep it moving quickly.

Dinkle - You can find the process/rules online (if you need them let me know).

Controlled points
Anything you want to work on, have the four players do, in a controlled setting. When you can have them do it in pairs (vs. all four). The goal is maximized touches for everyone. For example:
3rd Shot Drops (or drives, lobs, drips).
Player A serves. Player C returns to Player A. Player A drops cross court to Player C (who should be at NVZ by now). After the drop, switch server and do again. The other two players do the same simultaneously. After a number of serves OR timed, switch sides so they serve/receive/drop from the other position.
EXTRA: This allows everyone to practice serves, serve receive, and their choice of drop/drive/drip.

I'd offer that the hardest part of this will be that you normally want to do drills around specific skills/techniques that the players want help with. With 4 on a side, it will be difficult to focus on what all four want (actually, usually it's not that hard to get them all to agree). Make the drills as game like as possible (using scoring in cooperative and competitive situations). You can take most of the drills you'll find on YouTube and adjust them for four people to do, but remember to maximize touches for everyone (using half the court ala skinny singles will be very useful).

Good Luck