Hi, I've been playing some households in rotation. Whenever my sim visits his parents house, the hamper is always full but never use the washing machine. So I don't expect them to do themselves, but I want to have my sims help laundry for them. I don't see any interaction on inactive family's laundry pile or washing machine. Is there a mod active household can use the washing machine in neighborhood? thanks for all helps.

Try giving your sim the "Inappropriate But In A Good Way" reward trait as well, as this helps with allowing them to perform a lot of actions they would otherwise get thrown out for, but I doubt they will be able to do laundry that is another households. It might be worth a try though

Sims in inactive households will always look after their own needs eventually

I tried that sleep over option but still can't do it. Even though I have neat sim in other household, he always put the laundry away to hamper, and never run the machine. When the hampers are full, then the sims just leave the laundry on the floor, then do nothing. I think because they can't do anything while being invisible in their house. This is what I found so far, so I just want to help their work.

Most of my sims have that reward. The reason is that there's no option for 'laundry' on washing machine in other household. So I wish to have that 'laundry' option for the washing machines in neighborhood house. Would it be possible?
One time, I saw one of my played sim doing the laundry in his dad's house while being inactive. But there was NO option for laundry for the active sims. I wondered how he could do that with only free will.