Recipe: Safely Canning Beans with Potatoes

You would need to follow the instructions and times for onions, which is processing for 40 minutes in a pressure canner. You use the time for the ingredient which has the longest processing time, which is the onions...
I would also do the potatoes as recommended below, precooking them.

POTATOES, WHITE - CUBED OR WHOLE

Quantity:
An average of 20 pounds is needed per canner load of 7 quarts; an average of 13 pounds is needed per canner load of 9 pints. A bag weighs 50 pounds and yields 18 to 22 quarts - an average of 21/2 to 3 pounds per quart.

Quality:
Select small to medium-size mature potatoes of ideal quality for cooking. Tubers stored below 45 F may discolor when canned. Choose potatoes 1 to 2 inches in diameter if they are to be packed whole.

Procedure:
Wash and peel potatoes. Place in ascorbic acid solution to prevent darkening. If desired, cut into 1/2-inch cubes. Drain. Cook 2 minutes in boiling water and drain again. For whole potatoes, boil 10 minutes and drain. Add 1 teaspoon of salt per quart to the jar, if desired. Fill jars with hot potatoes and fresh hot water, leaving 1-inch headspace.

Your green beans may be overcooked, I have never tried it.