I have some ideas to help the issues on small tribe servers.
1. Fertilized eggs can only be picked up by the tribe the dinos belong to. This includes when a player drops one, it can only be picked up by that tribe.
2. Dinos cant be reclaimed.
3. When a tribe is being attacked, their dinos and structures are protected for 24 hours from other tribes except the one attacking. Meaning if a structure is destroyed or a dino is killed the tribe being attacked will be protected from other tribes for 24 hours. Timer resets everytime a structure is destroyed or dino is killed.
4. If someone leaves or gets kicked from a tribe, they can no longer join that tribe.