Hi mate54 I've just placed another copy of the Family Farmhouse lot, moved the Newson family in and tried again and this didn't happen, but going back into the Broke's on their Family farmhouse it was still doing the same thing even after closing and re-opening the game (Steam edition). With the Broke's Version of the house, it seems to do it with any Fireplace that's placed (video 2), not just the one that's included in the house.
To test further, I've just moved the Broke's into the copy of the family farm house that I tried with the Newson Family, purchased a fireplace and the same thing is happening (Video 3). I then moved them to 170 Sim Lane and the same thing happens there too so appears to be following the Broke family round in my game.
The only content I've added to the game are 2 or 3 lots, but they were all made with Sims 2 content, nothing custom and I've not used them yet. There was a widescreen menu mod I tried but that didn't seem to work with this version of the game so just put the original file back and am currently playing vanilla. Other than that I've only used "Aging off" and "Maxmotives" cheat a handful of times for the Broke household. I've possibly used "Boolprop testingcheatsenabled true" at some point to reset stuck sims in the household but usually set it back to false again when I'm done with it