(Replying to your blog: Help me Aunt Anne, Not that I'm Aunt Anne of coz :p)
Hello...
Out of the 3 solutions u listed out, I think the most feasible one is No. 2 - where you have to talk to Lisa your concerns and state your stand. You don't have to feel embarrassed actually. Because though you want to respect her as an adult, you gotta know that you are the Landlord and has the right to make things clear (the rules & regulations she has to abide as a tenant). It's just like employer and employee, it's perfectly fine (I feel) to have some kind confrontations once in a while.
To add on, Daniel has also stated his stand that he wants to continue renting out the room. You may want to ask Daniel if he wants to speak to Lisa or both Lisa & Alvin on your behalf. But from the experience I have with my hubby, I realised that men don't really like to do these nitty gritty things - especially when it has to do with domestic affairs. So this is the part when wives have to step in and play the role of the one handling the domestic issues. So why don't you find a chance to sit Lisa down (w/o Alvin preferably) and state your stand and your concerns. I believe things will improve. And if you can settle this, I think Daniel will be super proud of you.. And things might not be that difficult to resolve as what you think :)
If there's still no improvement, I suggest that you change the lock and pass 1 key only to Lisa. Haha... no lah (this will be the last resort).