Sister wants to move in?

Hi. Everyone today I want to ask a question. Do you think it is a good idea to rent to family? Why or why not? Here's my situation I have a sister who always looks to me for advice. At this point she is having problems with her landlord and by me being a landlord of course she came to me.  She moved into a house and at the time it was warm and she didn't know that the furnace didn't work.  So she lets the landlord know and he says he would get it fixed but that was two weeks ago. She now tells me that she didn't pay him the rent and he is threatening her to evict her.  I told her technically its his property and its his right to evict her because he owns the property and she still has to pay. She needs to go about things the legal way; pay rent, call the building inspector (the city) and take him to court.  The landlord is in the wrong and should provide at least some space heater. But back to my question do you think it is a good idea to rent to family? At what point should family be family and business be business?

I have a a tenant that I call Old Faithful (which means they pay on time and been in building since I opened in 2009). They called me and told me that they are having financial problems and asked could they pay me a little late.  Now I agreed to give them two weeks.  Now the two weeks have come and gone and no call. What should I do?