Primary 1 registration under 2CS

Hi, can I check if we were to apply primary one registration using our own address under 2C but did not get in, under 2CS, can we apply under the grandparents place instead. Our address and grandparents address is different area( one North area, one at East area). Kindly advise the procedure how to go about in applying and if it is possible to apply under 2cs with grandparents address if 2c phase fail to get slot in school. Thanks in advanced