My sims won't go up there stairs in this townhouse build.

So, I downloaded this house from the gallery. My sims were able to go up the stairs just yesterday, but they won't use the stairs today. It's a for rent house, so there are other units attached to this lot. The other problem I was having was that my sims wouldn't go to certain parts of the room. I moved stuff around to my liking. But, I was thinking since the layout was already done maybe it won't let me change the layout. So once i fixed that, it worked. I went to play my sims, and in any of the units were my sims able to go up there stairs.

can someone please help me?