Help guiding my dad to assisted living

My dad really needs to go to assisted living. Some of my siblings don't want to force him, but we can't monitor him 24/7. My sister had to take him to the ER last Sunday for dehydration, 2 full IV bags and still didn't need to pee.

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The problem, is he's refusing to go, or even admit he has Alzheimer's... he does, he asked me what his fingernail was last week. Any advice on how to gently force the move?