Which Hawaii island to visit?

Hey All,

Currently looking into a family trip late August (~7days), all adults however one cannot do long distant walks/rigorous trails. This will be our first trip to Hawaii but for some will be there only time to visit :(

Based on the countless forums, blogs, sounds like Oahu has a bit of everything for all types of adventures (city life, nature, beaches, food). The other contender is the Big Island for it's volcanoes and vast nature.

Is Oahu the best bang for our buck that will provide the Hawaii experience?

Is it worth looking into inter-island flights with only 7 days?

Open to any suggestions/recommendations to help narrow our choices.

Thanks!