@HumbleBee - thanks so much for your advice. I called back and indeed, the other agent had no problem issuing the tickets with 9 segments. I also booked another ticket with similar itinerary except that it departs from LAS instead of IAD. So this new ticket has two open jaws and one stopover, no problem asked.

Thank you all who have replied. I checked the price for this itinerary for July, and it costs around $5000. I couldn't believe I could get it for 65,000 mile plus $62. The UA miles are really valuable!