for( Opportunity opp : opportunities ){

            // when individaul account has a household account
            if( mapAccountIndvAccIdToHouseholdAccId.containsKey( opp.AccountId )){

                Id householdAccountId = mapAccountIndvAccIdToHouseholdAccId.get( opp.AccountId );
                if( householdAccountId != null ) {
                    Opportunity oppToUpdate = new Opportunity( Id = opp.Id, AccountId = householdAccountId );
                    mapOppToUpdate.put( oppToUpdate.Id, oppToUpdate );
                }
            }