Does the guardian grandmother retain the bail money received for each of her minor grandchildren individually, or does she collect it for them jointly, knowing that these are individual bails and they eat together?

If the sponsorships provided for orphans are equal, there is no need to differentiate the money of each one if they are equal in spending on them. However, if the sponsorships or spending differ, the money of each orphan must be differentiated. It is permissible to mix their funds for spending and trading with the surplus, based on the saying of Umar ibn al-Khattab: "Invest the orphans' money so that zakat (definition) does not consume it." The purpose of this is to grow the orphans' money, not for the guardian to invest it for their own benefit.