On the tree-shaped plants, you’re going to see many, if not most, of the leaves fall off. That’s fine if the buds on the branch, at the base of where each leaf was, aren’t also dead. Since the cold was for only one night, there’s a chance that not all of the buds were killed. The buds will send out new growth within a few weeks. If the bud at the end of the branch dies, other buds will grow—kind of like if you pruned the end of the branch. If the branch tissue was also killed, then even if the buds start to grow, they will not last.
The peace lily and mother-in-law’s tongue plants grow from crowns and rhizomes at or below the soil level. An overnight freeze probably didn’t kill the buds at this level, so cut off all of the dead leaves and watch for new growth.
Plumerias grow outdoors in Southern states, where they’re exposed to cold temperatures during some winters. They lose all of their leaves in the winter and grow them back in the spring. Being outdoors, they go through the fall, and they can handle the occasional cold spell. Your plant was exposed to a quick drop in temperature and may not be as ready to handle the cold. I expect it to be fine, but it may not send out new leaves until spring.
Prune out all dead leaves and any branches that are obviously dead. Leave anything that might make it to see what happens. This way, you can see if the plant is continuing to die or is starting to recover.
Don’t fertilize for a few weeks, as we don’t want to burn any roots, and this isn’t the time of year to promote too much growth. If the plant is dead, you would just waste any fertilizer on that plant. Water as usual, except don’t overdo it on plants without very many leaves.
