Three siblings own property in Michigan as joint tenants with rights of survivorship. One person wants to sell their portion of the property to one of the remaining kids. Will that give that one person 2/3rds right and the other one 1/3 right or do the remaining two still own it 50/50??
This really is a legal matter rather than a money matter.
Each sibling doesn't "own" 1/3rd of the property; together, the three own entire property jointly, and if one or two siblings pass away, the survivor(s) own the property in its entirety. That is, a sibling cannot make a will leaving his or her "share" to his or her spouse or children etc.; that so-called share is automatically divided among the surviving tenants.
To do what you want, the three siblings must terminate the existing joint tenancy (requires the consent of all three joint tenants) and create a new tenancy in common with one sibling owning a 2/3rd share and one sibling owning a 1/3rd share and the third completely out of it. At that point, the sibling owning the 2/3rd share will pay the one getting out of it whatever cash value is agreed upon. There will be tax consequences depending on which country's (or state's) laws are applicable to the transaction.