Well, Princess Astrid and the late Princess Ragnhild stopped being members of the Royal House when they married ''non-royal'' men.
The media didn't want this to happen to Märtha when she married in 2002, but the King meant it would have been unfair to his sisters if she had retained her position, while they had to let go of theirs.
That means:
They are no longer Royal Highnesses.
Their birthdays are not an official flag day anymore.
They are no longer on the balcony on May 17th.
They are not required to perform royal duties.
They does not receive money from the state.
They have to pay taxes.
It was the same with Sverre. The King and Haakon meant it would have been unfair to Raghnild, Astrid and Märtha if he was to retain his position after he marries. So, therefore, Haakon and MM thought it was best that he was born without being a member of the Royal House, because then he don't have to go through the same process as the princesses had to do, when they lost their positions.