According to the HH terms and conditions rewards are limited to double occupancy.
Hotel Reward Stays apply to full Point redemptions or Point redemptions combined with money. Redemption stays can be used for Standard Rooms or Premium Rooms; both Reward types are for double occupancy room rate. Additional occupants, age 19 and above, are subject to the standard extra person charges.
It's not unusual for redemption and money rates to increase when you add additional persons at some properties and it often makes a difference if the additional persons are adults rather than children. I think I would book the two rooms and contact the hotel (or use the new tab for connecting rooms if offered in the app)and ask for connecting rooms.
See also:
https://www.flyertalk.com/forum/hilt...=#post33025664
Reward booking non available rooms
Hilton Rooms for 4 adults