If my child has to fill her 1st declaration, can I add her to the one for myself and husband or should fill one separately for transfer of school expenses

If you need to transfer tuition from your child to yourself, then you would need to add them to your return as a dependant.

This FAQ tells you how to transfer unused tuition credits: https://turbotax.community.intuit.ca/community/family-education/help/how-do-i-transfer-my-unused-tuition-credits-to-someone-else/00/873652

This FAQ tells you how to enter tuition transferred from a spouse/partner or a child: https://turbotax.community.intuit.ca/community/family-education/help/how-do-i-enter-tuition-transferred-from-my-spouse-partner-or-my-child/00/873447