Ok, here's an update. I spoke to my mother by phone today, and agreed to loan her money on the existing house, enough for them to buy the double wide. So that would be about $90-95k. She will pay interest at the minimum level mentioned earlier in the thread, followed by a payoff of the full amount when the house is sold.
I brought up the points about interviewing 3 brokers ASAP (within the next month), having family help with emptying the house, and that basically the idea of waiting a year to sell is ridiculous, and she needs to put in a lot more (mental) effort in getting ready to sell.
I will be contacting a couple of real estate and lawyer friends in the area for advice on hiring a lawyer to help me with writing a mortgage, registering documents, and whatever else I need to do. I came up with the brilliant idea that I will hire an appraiser to give me an appraisal on the existing house, in case it's worth less than the amount I'm lending. I will be covering the costs involved with setting all of this up.
In terms of long term, she has income of about $30k/year, is the sole beneficiary of her husband's will, and does not have a will herself (lol). She will be drawing up a will as part of this whole mess. He has a 60k retirement account that he is taking minimum required withdrawals, Social Security, and a part time job, which he will keep for about 5 more years. She does not know whether her Social Security payments will increase or stay the same if he predeceases her (which is the expectation). The payments for land rental and taxes will be about 700/month at first, to be split equally between the two. Even if/when she has to pay the full amount, it would be 28% of her income, so it seems sustainable. In addition, if the house sells for $160k, that would be a cushion that could be used later or put into an annuity.