The first step you should take, before actually starting the conversation, is to talk to all involved family members to make sure you are all on the same page. Resolve any misunderstandings or disputes ahead of time so that you can approach your parents with a united front. Doing so will likely reduce the risk of putting your parent on the defensive. This doesn’t mean the entire family needs to be in on the conversation.
The planning is much easier if your parent still has some decision-making capacity. In that case, the next step is talking with an elder law attorney to discuss the elements of the estate or incapacity plan that need to be included. When there are several siblings, for the purposes of transparency, it is best to have all of the children participating in the discussions if at all possible.