I wish there was a way to prevent a sibling from convincing a parent to give them everything. Unfortunately, undue influence is hard to stop and ends up being litigated after death.
If a client comes in to Geisler Patterson Law wanting to favor one child over another, I encourage them to tell their other children of their plans in person. I also make them write out their reasoning in a letter or video.
I have discovered that if the reason is truly logical (one child has cared for parents for years passing up opportunities and truly deserves more), parents are willing to tell their other children who support the choice. When the unequal gift is being unduly influenced, my clients have trouble giving their reasons. In that scenario, if they can’t provide reasons, I tell them they need to find someone else or think about it longer.
Sadly, a child trying to get an estate has many options to get a legal document. Online “do it yourself” services don’t care; non-attorneys have no duty to the person who will be signing the document so will do whatever someone pays them to do.
Is the situation hopeless? NO. Understand the first Red Flag is ISOLATION, so do what you can to make sure you stay involved in your parents’ lives. That is your best defense.