Is it permissible for the supplication when slaughtering the aqiqah for the youngest granddaughter to include all sons and grandchildren, and what should be said at the time of slaughter?

It is not permissible to share one sheep for the 'Aqiqah of more than one child. There is no specific supplication for the newborn at the time of the 'Aqiqah, but there is no objection to supplicating for the new baby and for other children with whatever one wishes, as long as it does not involve transgression.