What is said to the family of the deceased in condolences, and what is the ruling on saying, "May your head be safe" or "The remainder is in your life"?

There is no harm in such phrases, but a Muslim should not substitute them for praying for the deceased for forgiveness and for the afflicted for reward. It is recommended to pray for the deceased with what benefits them, such as: "May Allah magnify your reward, may Allah make your solace good, and may He forgive your deceased."