Does an Agfa Isolette have a threaded lens to accept accessories? You may have to go with an old 'slip on' adapter, and then find the right parts to adapt the wide angle adapter. The other problem is the viewfinder. You might find an old accessory wide angle finder to go in the accessory shoe.
The whole thing looks kind of awkward. My suggestion would be to find a different camera for wide angle work. In 35mm you might find a Yashica GSN with the telephoto and wide angle adapters and the matching accessory viewfinder. It's not real wide, about equal to 39mm on a 35mm camera. I'm just thinking of cost here. Just my two cents worth.