When Frostcrag reborn defence is active you and Vilja take damage before even the cell is fully loaded.
The problem is from Vilja taking damage. And it's a trap, so there's no protection for her or you. I've found the problem and we will update her script for the next release because there might be other locations that have a similar problem.
But for Frostcrag Reborn, I suggest a work-around relating to your observation that:
With this defence system active, you take damage everytime you enter your own house. Considering that you can teleport yourself to this location and that you or one of your companions could be seriously wounded the moment you decide to cast the teleportation spell, I don't see the point of keeping this "defence" raised.
I fully agree that having the defense active in the spots where you enter the tower is extremely annoying. It turns out you can fairly easily disable just a small part of the defenses so that you can get in the door or teleport into the space without creating a crash.
First, turn on the tower defenses and go stand right at the front door facing the center of the room.
Open the console, click on the cloud in front of you and type "SetPos Z -300"
That should disable the trap with formid xx01592B, so close the console.
Use the teleport spell, then turn around to face the main door.
Open the console, click on the cloud in front of you and type "SetPos Z -300"
That should disable the trap with formid xx016CFF, so close the console.
Of course you'll still take damage when you move through other parts of the tower, but at least you won't get blasted as you arrive and so you shouldn't get a crash if you arrive with Vilja. You could also move the teleport marker up onto the platform near the cutoff switch, but you'll need to use the Construction Set for that since the marker is invisible.