Nobody likes to sell the farm. But there’s got to be someone there to take care of it and him. If there isn’t, then yeah, sell the farm and he gets to move in with someone who can care for him, either family or an elderly care facility. (And you really don’t want your family in a care facility.)
Yes, high concentrations of anything aren’t good for you. That study found a negative effect at comparatively high levels, but did not quantify any safe level, let alone conclude the safe level is zero.
Based on known performance in areas with lower fluoridation (≤1 mg/L), it would suggest there is a safe limit that can improve dental health without neurotoxicity.