Home Cleaning Routine

Btw, did the fumigation remove the infestation completely?

 

Yes, after that there was not a single insect in sight for years, leave alone bed bugs. Even cockroaches and other small insects too were nowhere in sight for years. Only now, I am having problems with red ants in the kitchen inspite of all the cleaning - i need to find a solution for that only. I agree the smell lingers for almost a week after the process, and it would be difficult for a very old person to bear this. So, try the deep cleaning and normal pest control at first and see how it goes.

 

You can set an example. Once it is very well organized and clean, invite them over spend time in your place. They might like what they see.
Does your SIL lives with you? Then you can volunteer to help organize. Once she sees what you have done, she might be ready.
True you have no right to throw their stuff.
Once your SIL's things are organized, you both can work on rest of the stuff. While organizing, you can separate things such that all the throw away stuff in one pile and let them decide what they want.