To keep him from death. the pharaoh though there were too many Hebrews and decided to kill the new born male babies.
Moses' mother, Jochebed, did not have to give up Aaron because he was born before the decree to kill Hebrew male infants. When Moses was born, the Pharaoh's order was already in effect, prompting her to hide him to protect him from harm. Jochebed's decision to safeguard Moses allowed her to keep both children, as Aaron was already older and not subject to the same immediate threat.
At the time, Pharaoh was having all of the Israelite boys killed to slow down the growth of the Jewish nation. (Exodus 1:7-10 & 22) (New World Translation of the Holy Scriptures)
The phrase "no yeah no" is used as a filler or hesitation in speech, and may not have a specific reason behind it.
Because he will need it in the underworld,
Possibly derived from another saying "keep your shirt on" ie meaning that taking your shirt off is what you do before settle an argument by fighting.
The Egyptians had decreed to kill all the newborn Israelite boys. Moses' mother hid him for three months (Exodus ch.2) in the house, but later found herself unable to do so (ibid). She then placed him in a waterproofed basket in the river bullrushes (ibid), in the hope that God would provide some form of rescue for him, and that is what happened.
The Ark
she could not keep him
Keep reading on.
They keep them inside temples
Don't lose your head would be a way of saying, try to keep your cool during a rough time. Try to think clearly. .Remain calm .. Keep your head and focus beyond the current crisis.