The situation you are describing is similar to other situations I hear about in my counseling practice with older adults. These kinds of dynamics occur in some (but certainly not all!) families and play out in several variations on this theme.
Motives for the controlling behavior on the part of adult children are not the same for everyone. Most frequently, there is an underlying theme of genuinely wanting their adult parent to be safe and properly cared for, but in some cases the motive arises from parent-child relationship issues from long ago that have never been addressed. Unresolved anger and hurt residing in the adult child and shared with their spouse can lead to a distorted portrayal of the parent. And, let’s face it, some elderly parents can also be difficult, controlling, and have unresolved issues with their adult children. The road often goes two ways.
Regardless of the origin of the difficulties, older parents and adult children are both responsible for trying to communicate and create a healthier dynamic in the relationship. However, sometimes the dynamics of the relationship are so entrenched that they cannot be successfully altered without outside help from a counselor or geriatric professional.
In your situation, the perception of diminished capacity is inaccurate and sounds like a pretext for control and the expression of anger. You do not have to put up with this type of treatment. The son-in-law’s frequent expressions of rage and both adult children’s consistent criticism and devaluing statements cross the line into verbal and emotional abuse and this situation calls for intervention if you cannot work it out with them by yourself.
While any single comment or fight or act of control would not be likely to be considered abuse, an ongoing pattern of such behavior would fit the definition. If you are capable and pretty independent, you can make choices as to how much time you wish to spend with the family and how much information you wish to disclose to them. It is important to protect your autonomy unless or until you truly need help. For older adults who are not capable of managing all of their own affairs it is important to line up assistance, but this may need to come from people and agencies other than family. In either case, drawing clear boundaries around acceptable behavior and treatment of one another is absolutely essential.
It is important for you to establish new norms at this stage of the relationship with your adult children; otherwise this behavior is likely to persist and worsen over time. If you need help with the situation, I strongly suggest you consider short-term counseling to get support and brainstorm strategies for dealing with the family situation. Help may also be available through the Area Agency on Aging, Human Services agencies that deal with elder abuse, and the numerous programs for seniors available in this area. Fortunately, we are rich in resources here in Northern Colorado. I wish you the best and encourage you to empower yourself and do whatever is needed to limit or reverse the damage that is occurring to you and to your family relationships. There is a lot that can be done. You need not feel hopeless.