I've done this before. We just played on lichess analysis board with the engine and database turned off
Most Recent
Forum Legend
Following
New Comments
Locked Topic
Pinned Topic
To play on the same device with someone else, you must click the "more" tab and hover over "other" in the more tab. Then, move your cursor to the window that opens up and click "explore" and you should be able to play co-op on the same device! hope this helps : )