Most likely they are invited, Rudolph. The Queen don't have senior royals to meet and greet the Head of State and have them escort the Head of State to the welcoming ceremony and then don't invite the same senior royals to the State Banquet later in the evening. If Charles & Camilla, Anne & Tim or Edward & Sophie meet and greet the Head of State and escort them to the welcoming ceremony and attend the reception at Buckingham Palace or Windsor, you better bet they will be attending the State Banquet in the evening. They don't do things halfway.
Again, it's understandable if Catherine isn't able to handle the State Banquet in her condition but let's get real here-they should be going to the State Banquet too.
I don't criticize William & Catherine often but they have to straighten up and fly right when it comes to carrying out their duties at State Events. Every excuse was made for them in not attending the Obama State Banquet, they didn't attend last years State Banquet and now it's being said that they won't attend the Singapore State Banquet. Just silly stuff, IMO. Every other royal -who's not even close to the throne and minor- attends the State Banquets but it's like pulling a dinosaurs teeth to get the second in line to the throne and his future Queen to attend.