Show multiple joined rows
Try using aliases like this:

SELECT l.*, c.*, u1.*, u2.*
FROM log l
LEFT JOIN cars c ON l.car_id=c.car_id
LEFT JOIN users u1 ON l.user_id1=u1.user_id
LEFT JOIN users u2 ON l.user_id2=u2.user_id


(Note that it's bad practice to use "SELECT *" except for ad-hoc queries. So you should instead enumerate the exact columns you want to select.)