diff --git a/backend/internal/handler/user_handler.go b/backend/internal/handler/user_handler.go
index 147e85e5..ea522069 100644
--- a/backend/internal/handler/user_handler.go
+++ b/backend/internal/handler/user_handler.go
@@ -103,13 +103,16 @@ func (h *UserHandler) ListUsers(c *fiber.Ctx) error {
 	if requesterRole == domain.RoleTenantAdmin || requesterRole == domain.RoleUser || requesterRole == domain.RoleRPAdmin {
 		profile, _ := c.Locals("user_profile").(*domain.UserProfileResponse)
 		if profile != nil {
+			var baseTenantIDs []string
 			for _, t := range profile.ManageableTenants {
 				manageableSlugs[strings.ToLower(t.Slug)] = true
-				manageableSlugs[strings.ToLower(t.ID)] = true // Add ID as well
+				manageableSlugs[strings.ToLower(t.ID)] = true
+				baseTenantIDs = append(baseTenantIDs, t.ID)
 			}
 			for _, t := range profile.JoinedTenants {
 				manageableSlugs[strings.ToLower(t.Slug)] = true
 				manageableSlugs[strings.ToLower(t.ID)] = true
+				baseTenantIDs = append(baseTenantIDs, t.ID)
 			}
 			// Include primary tenant slug if not already there
 			if profile.CompanyCode != "" {
@@ -117,6 +120,47 @@ func (h *UserHandler) ListUsers(c *fiber.Ctx) error {
 			}
 			if profile.TenantID != nil {
 				manageableSlugs[strings.ToLower(*profile.TenantID)] = true
+				baseTenantIDs = append(baseTenantIDs, *profile.TenantID)
+			}
+
+			// Expand manageableSlugs to the entire tenant tree (root + all descendants)
+			if h.TenantService != nil && len(baseTenantIDs) > 0 {
+				allTenants, _, err := h.TenantService.ListTenants(c.Context(), 10000, 0, "")
+				if err == nil {
+					parentMap := make(map[string]string)
+					for _, t := range allTenants {
+						if t.ParentID != nil {
+							parentMap[t.ID] = *t.ParentID
+						}
+					}
+					
+					// Function to find the root of any given tenant
+					findRoot := func(id string) string {
+						curr := id
+						for {
+							p, exists := parentMap[curr]
+							if !exists || p == "" {
+								break
+							}
+							curr = p
+						}
+						return curr
+					}
+
+					// Collect root IDs for all base tenants
+					roots := make(map[string]bool)
+					for _, id := range baseTenantIDs {
+						roots[findRoot(id)] = true
+					}
+
+					// If a tenant shares a root with any base tenant, it's in the same tree family
+					for _, t := range allTenants {
+						if roots[findRoot(t.ID)] {
+							manageableSlugs[strings.ToLower(t.Slug)] = true
+							manageableSlugs[strings.ToLower(t.ID)] = true
+						}
+					}
+				}
 			}
 		}
 	}