Sister recently back in family picture & has taken over except for one major item. Any advice?

I have posted here before but it's been a few months. I will try to be brief.

I am 61, my sister 65 and Mom 90. Sister came back in the picture about 2 years ago after being gone for 20-30 years with little contact. She came back in 2000 when Dad had cancer and passed demanding we sell his small farm then. I shut that down as I told her it wasn't hers to sell it was Mom's. Sis left shortly after his death back to hiding in Florida until recently as Mom is failing. Of course she smells green again which brought her back. At this point she has brainwashed Mom and turned her against me and my family, her only 2 grandchildren. This has been going on for about a year plus now and continues to worsen. Sis demanded months ago that the will and property be divided to a greater proportion to her than what it had been set up with Dad and Mom years ago. I actually had no idea how it was set-up or divided but had heard Dad talk about it once in awhile. I worked the farm with Dad to pay for my College education - it was hard work but made me what I am today. Dad's last words to me in Hospice was to hang onto to the farm as long as I could. See he was an orphan as a child, then a factory worker and the farm was his life's accomplishments besides his family. It meant alot to him and to me. Come to find out the deed's to their house and main portion of the farm was in my name with a Life estate for Mom. Sis had 10 acres. Needless to say when Sis found this out it has been hitting the fan ever since for the past year. She has taken over most all of the other accounts and is now POA. Mom has $150k-$200k in debenture bonds which were split up equally to me, sis and my 2 grown children. I am guessing they are all in Sis's name by now. Sis has basically blackmailed and brainwashed Mom to the point no one in my family can communicate with her. Sis has gone through several high power attorneys trying to force me to sign back over the house and main portion of the farm. This is my only card in all of this mess. It has been very stressful to me and my family, day-after-day for the past 1+ year since Mrs. Wonderful (& #4 husband now) returned. I do not want to sign off as I know exactly where it will go. See the farm sits on a new interchange and could go commercial. Sis already is seeing green and wants to cash out per say and go back to Florida in hiding again. Sis has been communicating solely through my country attorney as I refuse to talk to her and have disowned her as I am so disgusted with how she has stolen Mom from me and my family. I just don't need the constant stress and would like to move on with what remaining years I may have as I recently retired. Sis sent my attorney an email recently demanding I sign off because Mom is failing and may have to go into a nursing home and would like to sell the house. She is proposing 30% go to Mom. Not sure where the rest of it goes or if she is proposing it be split between me and her. I would assume I remain on the deed to the major portion of the farm. I realize there are a lot of unknowns here and am moving very cautiously. Sis gave a deadline of June 23rd. Of course my attorney said I can simply ignore her as I don't have to do anything. I am concerned though if they abandon the house and it goes into disrepair. I also look at this as an opportunity to get some or all of this monkey off my back so I can "live" in peace. I do not feel right in taking any of the house money as I have always stated it should go towards Mom's care if needed but with a hands off for sis on any of it. Mom does have very good long term care/retirement home insurance that she has been paying on but I would assume it will not cover 100%. My initial thoughts are to create a trust for Mom with the sale of only the house with myself as the guardian or trustee with no way Sis to get her hands on it even after Mom's passing. The farm would remain deeded to me without the life estate also at that point. The rest of the inheritence is gone in my thought as Sis has all of it in stone by now. I am concerned with upholding my Father's last words and hanging onto the farm as long as I can. This is what he wanted and entrusted me to do. What are your thoughts on the trust portion or any other advice anyone could provide? I have found there really is no one to lend an ear on things like this, although I am thankful I have a good attorney. Of course my attorney would tell me and has, don't give up anything. Thank you for your time if you should choose to reply.