Right, so I examine the 'badly damaged' field emitter with the Science skill, and it says the field is weak enough to walk through. I walk through it, take a small amount of damage because of my Hardened Power Armor, but my companions are getting fried to cinders because of poor pathfinding scripts (Dogmeat especially, as he just sorta saunters back and forth across the field until the damage turns him into a small pile of ash; so much for dogs being smart). Is there a way to permanently disable these fields, or at least get my companions to stay put?

I may just let them die, as late in the game as I am. They can't do enough damage to be of any help anymore, and are always blocking narrow halls and doorways that I need to pass through.

As far as I know you can't turn these forcefields off.
You had a lot of luck if you got your companions this far! It is extremely difficult to get them through the base though. Now, they can get one-shotted by pretty much everyone so either use a lot of stimpacks on them, or give them up, and let them die.

I think there are mods which let you order the companions to stay, but using them this far into the game might not work.

The companions were a last-minute addition to Fo1, they are a lot better in Fo2.

You can turn them off by using the computer on the first level. Another way is to use the radio on the computer and if you have enough points invested in repair, you can "link" the computer and the radio - using the radio will disable force fields. You can also use the tool on the force fields (or repair, if you have enough points it will disable it for a short while).

Another way is to use explosives - dynamite works as far as I can remember.

Just keep feeding them stimpaks.

I didn't know the trick with the radio. You learn new things everyday!
I'll have to do a replay soon :D