If a family member of mine has been left a life estate, and I have been left the remainder, what rights do I have?

The person left life estate is considerabley older than I am so there is more possiblility that they will pass before me and assumeabley the property is totally mine to do what I wish with it.
But what happens if I do die before the family member? Will they be able to take over the property legally and be able to sell or do what they wish with it? Or can I take actions now to leave this property to my wife and children in case I die before the person left the life estate?

Thank You for any information or advice on this subject.

Impossible to answer without seeing the actual language, so I suggest that you take it to a probate and estates attorney for interpretation. it sounds like you have whatever interest remains intact when the party with the life estate dies, but that could be in the life estate or it could be to the entire estate, whatever it is. It is just unclear and impossible to really answer because the drafting and intent are important to the interpretation.