LW#1, You sound a little passive aggressive. Why not just communicate your wants and intentions clearly? It was your choice to rent to them below market value, so don't blame them for that. You only hinted and did not say directly that you wanted to sell the house, so you can't hold that against them either. Further, the cancer diagnosis broadsided THEM, not you. It almost seems like you think it was personally against you. 

Simply tell them, in WRITING, that you intend to sell the house, and give them 60 days notice to move -- that would mean they are out before it's cold and they won't need extra heat (unless you live in the extreme north). Further, tell them in the same letter that space heaters and using the oven for heat are forbidden due to the safety risks. (That is actually not an uncommon stipulation in a lease). Make sure you have two or more smoke detectors installed. And if your house needs rewiring, you are going to have to rewire it before you sell it anyway.