Hi All. How to query for accounts in child territories? I can't seem to find any documentation for this 

Currently I'm able to query for the accounts in the current logged-in user's territrry only, but not from the sibling territories.

Following is my code...
 

public class TrackingPartners{

    public List<orders__c> orders {get; set;}
    public TrackingPartners() {   
    }
    
    
    public list<orders__c> getstart() {

    Map<Id,UserTerritory> UserTerritoryCurrentUserMap = new  Map<Id,UserTerritory>([Select u.UserId, u.TerritoryId, u.IsActive, u.Id  From UserTerritory u Where u.isActive=true and u.userId =: UserInfo.getUserId()]);

    
    
    set<Id> TerritoryIdSet = new set<Id>();
	
    for(UserTerritory ut:UserTerritoryCurrentUserMap.values())
    {
          TerritoryIdSet.add(ut.TerritoryId);
    }    

      list<Group> map_group = [Select Id, RelatedId from Group where (Type='Territory' OR Type='TerritoryAndSubordinates') AND RelatedId IN : TerritoryIdSet];


    List<SYSTEMS__c> lst_PartnersAcc = [SELECT CUST_NUM__c,Account__c
                                                 FROM SYSTEMS__c WHERE Account__c IN                                                  
                                                 (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:UserInfo.getUserId()) AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule'))
                                                 ];

                                                 
    Set<String>tempList = new Set<String>();

    for(SYSTEMS__c s : lst_PartnersAcc) {
        tempList.add(s.CUST_NUM__c);

        
    }
    
    List<orders__c> orders =[SELECT Orders__c,id FROM orders__c   
                                 WHERE  Bill_to__c IN: tempList OR
                                        Payer__c IN: tempList OR 
                                        Ship_To__c IN: tempList OR
                                        Sold_to__c IN: tempList
                                     ]; 
                                    

     return orders;                                
  }                                
  
}

How to query accounts from the child territory? Any reference would be great. Thanks in advance!