This is a known bug. If you have this bug please use the link below to share your experience with the bug and also to click the Me Too button below the the first post in the thread. This may help it get some attention and possibly fixed.
Sims unable to enter the house
http://answers.ea.com/t5/The-Sims-4-Bug-Reports/Sims-unable-to-enter-the-house/td-p/3462135/page/1However, there are some work-arounds noted below.
1. Check the house for possible problems; replace the front door and check the foundation of the house isn't too high - needing stairs.
2. Reset Sim - resetsim [firstname lastname]
3. If that doesn't work, evict the household and then move them back in. This in effect resets the household.
-- Go to manage world. - Evict current household. Then move household back into their house.
4. Switch active families. - Switch to a different family and then back again.
Edited to Add:
If your sims do get kicked out of their own home if you move them to another house, save the original house to your library, bulldoze the lot and place your house back down and then move your sims back in everything will be fine again and all their friendships etc will still be intact.