Life Estate, Revocable Living Trust

[hopalong]

My sister owns the property and wants to give me a life estate on the property and in case I pre-decease my sister she wants to give a life estate to my significant other with the ultimate goal of deeding the property to my significant others son who is 5 years old at present. Would you please help me to understand the steps that have to be taken in order to accomplish this goal. Does this have to be recorded. She wants me to have complete control over the property should she pre-decease me and give me the option should my significant other and I break up, however she still wants my significant others son to receive the property upon my death.