I know that Alzheimer's is a very difficult condition - for everyone involved.
What happens if at somepoint, their father is no longer able to take of their mom?
It about devastated my grandpa when he needed to have my grandma (who was suffering from Alzheimer's) put in a nursing home. Unfortunately, my grandparents were both 87 at the time, and my grandpa just couldn't physically help my grandma any more.
There are many wonderful nursing homes that have specific care units for Alzheimer's patients.
Until you have actually experienced someone who has suffered from Alzheimers, it really is very hard to comprehend the amount of work that this will entail. Assume at some point, an Alzheimer's patient will need the use of a wheelchair. (read - is your parent's home wheelchair accessible?) My grandma would wake up in the middle of the night, and would be disoriented, and would try to get out of her bed, and fall, and really hurt herself. This type of situation is monitored closely in a nursing home. In addition, nursing homes have patient lifts, and other assistive devices that can help caregivers get in and out of the bath.
I don't mean to sound harsh towards their father, there is no doubt he has the best of intentions. Unless he has a boatload of money available for them to get a private nurse, he is being unreasonable in this request.
Is it possible that the attorney allowed the language because he knew it was not enforcable once their father passes away?