I've had recent discussion with my lawyer with respect to similar question when it comes to Joint ownership.
BAsically, if property or bank accounts are held jointly , they belong to each other, so upon death, the survivor has full ownership, however, it can be disputed that the joint ownership was not really meant to be joint ownership, for example, Mom has her bank account, and she puts son Billy on the account and makes it Joint .... Mom then passes away and brother number 2 comes along (Pete) and argues that the reason for the joint account was not to give ownership to Billy, but Mom made him joint to make it easier for billy to pay her bills. The argument then becomes "what was the real intent that Mom put Billy's name on the account", or house or whatever that is joint. It no doubt can become a huge legal battle .
For this reason, it is wise to keep very detailed notes , even as far as visiting a lawyer while makeing the changes so th3ey can keep detailed notes.
Without getting into too many personal details, In my case, We visited my lawyer, he kept very detailed notes on the discussions that were happening with the family members involved and present, so if anything ever becomes contested, he would have his notes to fall back on, and therefor the reason for making the changes that were made .