My inactive sims inventory gets moved to family inventory even though I did the steps advised here:

Click on the City Hall Building/Map Tag or any computer
NRaas > Story Progression > General Options > Options: Money > Options: Sales
Disable the following by selecting them individually:-
Sell Crafts: Family Inventory
Sell Crafts: Personal Inventory
Sell Drafts
Sell Duplicate Inventory Items
Sell Duplicate Books

Click on the City Hall Building or Map Tag
NRaas > Story Progression > Town Options > Money: Allow Inventory Management
The default setting is "True". Change this to "False"

Its so annoying to be moving everything back and forth, is there something else I can do?

I think I figured it out, I think the settings don't protect the inventory items when you do a reset everything on your kinda laggy neighbourhood...

Oh yes, this happens a lot (to me) when resetting everything

You can bypass the active lot in MC Settings>Include Active Lot in Reset Everything>Set to False.
It's not the perfect solution if you rotate households though but it's one less.

I think I will just restrain myself from resetting everything and hope SP setting will protect sims stuff further. I spend 5 hours giving everybody their silly things back from family inventory and prefer not to do it again, or at least not for a very long time xD

While these types of things can be incredibly annoying, I do find that most of my worlds benefit greatly from a Reset Everything once every 6-8 sim weeks or so. Especially the busy, crowded ones. Becomes a trade-off when things like inventories then have to be adjusted. But it's not a procedure I would ever want to go through more often than that unless I was playing Isla Paradiso or some other world in need of constant help and corrective actions.