She poured cooking oil on the carpet, pulled the bathroom mirror off the wall, I'm not sure what she did to the bathroom sink but it may need to be replaced.

They have no need to turn off the sink, turn off any lights, or anything else.

Insulation is a reasonable investment, but beware: it is unlikely they're going to see huge drops in utility costs from insulating the attic, especially in cooling season (more likely to see a difference in the winter) because hot air naturally rises and cold air naturally sinks.

But, they knew they should have called you, in my opinion, on the leak under the sink.  

But again, just my opinion, my state (CA) is incredibly tenant-centric, so I'm pretty unforgiving, as one bad tenant could sink a property for me.That all said, I think she herself sounds fine, I'd just move forward with her and add him down the line, and I'd talk to her and make sure she understands she'll be held liable for the lease regardless of any breakup, joblessness on his part, etc.

If the carpet still sinks, I'll probably just replace that section.  

This would include, hardwood floors, granite counters, stainless appliances, double bathroom sink, open floor plan.I try to combine this with my wants as a landlord which is hard-surface floors and low maintenance everything.A couple examples, we use a lot of wood-grain vinyl.

@Ayana Lugo - as a PM, when a tenant places a service call to tell you 'my sink is broke' or 'my a/c is broke', 'my stove is broke', 'my lights won't turn on', etc - what do you do?  

Its MY money, My rental and I sink or swim by what happens with it.Again I agree with Andres you should try to work with the daughter.  

Or they might be more likely to call you when there is a drip beneath the sink, rather than wait six months until the sink cabinet base has turned to mush.