Is the first person who repented, and who planned the theft and pointed out the store's location, obliged to return the full amount (85,000 riyals) or only his share (28,500 riyals)?

All praise is due to Allah. May Allah accept the penitent's repentance, and upon him is to invite his two companions to repent. Sincere repentance requires abandoning the sin, regretting it, and restoring rights to their owners, based on the hadith: "Whoever has wronged his brother... let him seek his forgiveness today."

In the case of theft, the stolen item must be returned to its owner by any means. If it is impossible to reach him or his heirs, it should be given as sadaqa on his behalf. If the owner of the right appears later, he should be informed of what transpired. If he is content, then so be it. Otherwise, the value should be paid to him, and the sadaqa will be credited to him.

As for guaranteeing the stolen amount, the Maliki school of thought holds that anyone involved in the theft guarantees the full amount and can seek recourse from his partners.

The more probable view is that the repentant thief is only obligated to return his share of what he took from the stolen goods; thus, each participant guarantees the share he obtained.