In the North America, any will prepared by a law firm can still be challenged in court albeit not very common. Will like this that exclude family/children raises suspicion of fraudulent intent. Judge usually looks into it carefully and lean towards the plaintiffs. My HK aunt almost tricked into similar situations fortunately it was uncovered accidentally when she was already in dementia. The hospital informed us "who is this lady insisted on coming in with legal documents for aunt to sign?" during COVID-19 time.