Should I get guardianship?

This is one of the MOST stressful situations I have ever been in. I live in the US, grew up with my dad, and am now his health/finance POA. He is 88 with moderately advanced dementia and recent Alzheimers diagnosis. His wife, my stepmother, passed away 6 months ago and I have spent months of my 1st year of marriage away from husband managing everything for my dad, including making a comprehensive care plan for him as I live in another state. His other adult children, 3 daughters from first marriage who live in the UK, all of a sudden developed a greater interest in him after I had put his life back together and discovered he inherited a life insurance policy from his late wife. They wanted to know all the details of his assets and one of them decided she would buy a house in England but I, as his POA, would need to transfer most of his money immediately to her (40K) in order for her to put a payment on the house. At first, I was open to her plan b/c I thought he could be well looked after by his family in England, until I realized it was crazy to send all his money to buy HER a house in her own name, leaving him with no financial security. I spoke to an elder lawyer who told me that as POA I would be violating fidiuciary duty to send her the money. My father, given his mental state, would also waffle back and forth about whether he wanted to go. One day he'd say that such a big move would "finish him off" (and his doctors advised against it due to Alzheimer's), the next day while on the phone with UK family he would tell them how nice it would be to be there. They have done many crazy things like sneak out and take him to the bank when I am not around both to get his statements and to withdraw funds (claiming I am blocking him from his own accounts--NO, I am blocking THEM), threaten to kidnap him to England when I am not there (I heard this when one of them let it slip), having him sign a real estate contract to sell his house when I was out of town and then claiming that's what he wanted to do, telling him I am trying to institutionalize him when his carer/nurse is taking him to a routine doc appointment, making him have a mini stroke from the stress, etc, etc. The list keeps going. As soon as I head back home to my husband and work, they start calling incessantly convincing him I have bad motives and trying to get him to revoke my POA so they can get access to everything. Mind you, they have barely even been in his life for years and I have been taking care of him, and there for him for my entire life. Three of his doctors have each filled out medical reports that he is incompetent to make sound decisions and can no longer manage his affairs. They have all recommended guardianship, but of course he thinks he is fine and doesn't want it. I am considering going immediately for emergency guardianship to get the others to back off, but am concerned about a difficult proceeding if it's fought. I NEED to get back to my life. I am generally unable to relax anymore due to the major stress of constantly worrying what they will do next. He has said many times he wants to stay put but they want to move him to England and take everything he has. Should I go for guardianship? At times I feel desperate and alone in this situation. I used to be so close with my dad but I am even starting to resent him since he keeps telling everyone what they want to hear and perpetuating misery. Would love to hear from advice and ideas for how to get this situation under control and be able to relax and live my life again!