Here are a couple ideas of where to start.
Getting down to the wood:
There are a couple ways you approach poly/stain removal; one is chemical stripping and the other is stripping by sanding.
If there is a lot of detail to the table and chairs, chemical stripping might be the better way to go. There are number of great products out there and each has it advantages and disadvantages. I'd check with a pro paint supplier to get some recommendations - Sherwin Williams commercial etc. Of course this can be smelly and messy process. Definitely follow any safety precautions to the letter. Some of these chemicals are pretty powerful. Also, there are some good resources out there, YouTube etc, for help and tips with the actual stripping process.
The other direction you can go it to sand the finish off. This will take some elbow grease and power sanders like a belt sander, a random orbit sander, and possibly a detail profile sander. Some of these should be available at your local tool rental store if you don't own them. Start with a course grit sand paper, 60 to 80 grit depending on the thickness/toughness of the finish. Some finishes can become gummy from the friction of sanding. If so, change sanding paper often to keep removing material. When you get down to bare wood, work your way up to finer grits as you go, 150, 220, and even 320 for the final touch.
Hope that helps some.
Best of luck.