U need to have rock smash to beat it. then wait untill the girl turns, then walk by. after that dont run into the guy 1!
then there is the guy 2. u can aviod him by taking the grass. then there is the the girl 2. then hiker 1.
the guy 1: sandshrew lvl. 17
the girl 1: shroomish lvl. 18
the guy 2: zigzagoon lvl. 18 & nuzleaf lvl. 18
the girl 2: tailow lvl. 18 (again) & lombre lvl. 18 (agian)
hiker 1: geodude lvl. 16 & geodude lvl. 16 & geodude lvl. 16 & geodude lvl. 16
hiker 2: numel lvl. 18 & machop lvl. 18

hope i helped! :)