Have only one sim on the island so the NPCs have room to move
or engage the NPC with a secondary sim elsewhere
if that does not work, contact support - I know you have reached out to them before but there really is not something other players can help with
This forum is provided by EA but is designed as Player helping Player, in this case we can not do much for you
Contact support: Get there in game: green ... button at the bottom of the screen; info > online support
Or use the web https://help.ea.com/en/help-top-issues/?product=the-sims-freeplay
Or contact support via FB or Twitter, links are at the bottom of the page
