No, one owner cannot encumber (e.g. mortgage; take out a HELOC or reverse mortgage; etc.) a property without the consent of the other owners. If you and your siblings agree to let you (or all of you) tap the equity without selling, you can do that; but otherwise not. Without agreement of all the owners, your only recourse--and it is a drastic one--would be to file a "partition" legal action or lawsuit (your state may have a different name for it than "partition") in county court, seeking a court order compelling the sale of the property and the distribution of the proceeds among the owners. A forced or compulsory sale is the law's remedy when property owners cannot agree as to what to do with it.