Is your Mom still alive? Based on reading your post, I got the impression that she is.

1) My first thought is insurance.  IF you can buy insurance on her in the amount to buy the farm, that might be worth looking at.

2) I have read in years past about parents who have set up their will to give the farm to one of their kids, and to buy insurance for the non-farm kids to help even out the estate.  This is estate planning, and needs to be done up front.  You are probably too late for this.

3) A thought that crossed my mind.... talk with your Mom about starting to buy the farm now.  Set up a payment plan that you can afford.  This can be you, or it can be you and the one sister that has interest - if she has income to make payments as well.  Your Mom can make annual gifts to her kids.  So, she can take those payments that you are making to her, and make annual gifts to your siblings that don't want the farm.  And maybe she can gift some to your and your interested sister as well.  This might be a way to start the land transfer process before your Mom passes on.  If you want to consider this, you really need to run this by a tax specialist, to find out how all this would work in your situation.  It's a thought.