All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
It is permissible for you to offer the ‘Aqeeqah for your three children on the same day because you are making up for the ‘Aqeeqah, and there is no harm in offering it at any time.
Kash-shaaf Al-Qinaa’ (a book on Hanbali Fiqh) reads, “If the seventh day (after the birth of a child) passes without offering ‘Aqeeqah, then it can be offered on the fourteenth day, and if this day is missed, then on the twenty-first day. After that, (after the twenty-first day) one may offer the ‘Aqeeqah on any day he wishes because it is a make-up for a slaughter that should have been done in its due time, so it does not depend on a particular day, such as making up for the 'Eed sacrifice.”
Allah knows best.