Wuqūfan is understood as a circumstantial or cognate-accusative-style expression: the companions are in a state of stopping. Ṣaḥbī identifies those companions; the surrounding phrase locates them and their mounts near the speaker.
In lā tahluk, lā prohibits, and tahluk is a jussive imperfect. Tajallad is a command. The friends combine a prohibition ('do not destroy yourself through grief') with a positive imperative ('be steadfast'), making their consolation more forceful.