I have just called the centre. She said when we registered only the registered person needs to be the member of the centre. The others can join the membership later when the class starts.
But I note that we have 0701 - 0704 (I am 0704) babies. Is it ok since they need babies within 3 months. Mine should be the youngest born on Apr 13, he he. I think it is still ok to meet the requirement kwa.