Not all of the longhouses have balconies on the second floor level. They do all have balconies on their third floor level.
Reserving an 'MK View' room guarantees you an unobstructed view of the castle... but they may or may not also have a balcony. There are first floor rooms with MK views too--and these would have a patio.
You can request a balcony, but it will not be guaranteed. Ask/re-affirm your request again at check-in, and if an MK room with a balcony is available I am sure they will try to accomidate you.