Rudder, have your tribe leader set himself or someone else up with the permissions to loot all containers in your tribe radius via the totem menu, regardless of the status of the individual container. Pick up all the bags and trade them back-and-forth from someone else to yourself. Now you can set the permissions one by one on the bags to 'Tribe'. For someone to have a private bag, you need to trade them the container--just dropping it and allowing them to pick it up it does not make the bag "theirs" in the eyes of the game.

A container belongs to the last person it was traded to (or its creator, if it has never been traded). Only that person can set the permissions on it. If you can't open baskets in your own tribe area it is likely because someone who owned them set them all the 'private', but they can still be looted and moved by the tribe leader and anyone else with the correct settings on the totem menu.

Edit:
Coca, what is happening to you is likely to prevent strangers from interfering with a tribe's land; Baskets on the ground prevent terraforming and building near them, so any baskets on a tribe's land are owned, and thus movable by, the tribe. That is my guess, anyway. The permissions system is probably too primitive to handle multiple owners, so it kicked you out of your own bags. Have a friend who is still part of it pass the bags to you.