I am so sorry for the situation that you have found yourself in.I am no expert so i can only make suggestions for you to consider but as i am in Britain and i don't know where you are from then even these may not be of help to you.I will do my best though.
If it was me i would first of all go to your fathers doctor and discuss things with him or her.Will the doctor agree with you that your father would fall apart by being removed from the family home.My mother in law has dementia and i know that if she is taken away from her reguler routine and surroundings then she too would becme more confused and stressed.Things like being able to find the bathroom is a big thing for an Alzheimers patient.Also,and this may seem strange,but you need to be able to prove in court that you have lived with and taken care of your father for the last 7 years.Is it you that has always gone along with your father for hospital apointments etc,maybe you can get the doctor to give written proof of this.
Do you have a citizans advice centre or similer that you can go to? here they will be able to give you advice on the legal(sp?)side of things that you will need to have in court.Here in Britain we also have an organization called "help the aged"these people can be a great sorce of information and advice.
You say that your family has not helped at all in the care of your father but now want his assets,you will probably also need proof of this as well.Unfortunatly although you know what their intentions are they may be telling a different story,such as "Oh Mike has been living with our father rent free for this long and now it is our turn to have some benefit of Dads assets."
It is a difficult situation i know,and i do feel like my suggestions are a bit feeble for such a huge problem so i realy do hope that someone else will come along here that realy knows what they are talking about and will give you some advice.
Please post again and let us know how things progress,i can only say that i will be thinking of you.