بسم الله الرحمن الرحيم
(1) Read the following dua:
يا حي يا قيوم برحمتك استغيث .
(2) It is sunnah to keep the name of the child on seventh day.
(3) It is sunnah on seventh day. The relatives, friends and poor ones should be given to eat.
(4) Yes, both the names are good. You may keep them. However, the name of the girl should preferably be kept Yumna instead of Aimen.
Allah knows Best!
Darul Uloom Deoband