Sunburn doesn't heal - it leaves permanent marks on the leaves. Over time, new leaves grow and old leaves fall off or are trimmed, so we don't see it anymore.

Pcs 5 & 6 show what looks to me like necrotic spots. I would cut those leaves let the wound dry, then stick back in the pot. Lower light can yield spindly, weak growth.

Agree about the sunburn. When moving plants to outside, if the increase is not gradual and spread over some weeks, burning can occur. Starting with the first couple or last couple hours of daylight is usually safe, depending on how dim it was inside. Unlike people, plants do not heal from sunburn.

Pics 1, 3, 4 show what looks like soil that has a wet spot in the middle. Unevenly moist soil is not good. It looks inappropriate for epiphytic cacti. The nickname "cactus" can mistakenly lead us to believe they could or should have very little water. Epiphytic plants can get rotted roots (overwatering) so easily if the roots don't have enough oxygen, which is tricky because they suffer if the soil gets dry. A dense soil and impermeable pot are easy ways to kill them.

If you have the opportunity, I would encourage you to move these plants to clay pots and a much more chunky soil with lots of little air spaces. Avoid "potting soil" and look for somethng like "cactus/palm" soil. When changing pots, don't pack the soil, leave it loose, and water with a very gentle sprinkle the first few times so the force of gushing water doesn't compact the soil and ruin the tiny air pockets. All of the soil should be moistened, and excess water should drip out of the drain hole. After a few waterings, the particles should be stabilized in place.

They are naturally dangling plants, so a tall pot &/or a pedestal can be a great way to keep them. If you can happen to find a hanging pot that isn't plastic, that's great too. Something like a colander could be repurposed as a planter and although the metal is impermeable, all of those holes will provide access to oxygen for the roots.

Based on the pictures you provided, it appears that the Epiphyllum German Empress has suffered from sunburn, which can cause the leaves to become dry and brittle. Although the plant may recover on its own over time, there are a few things you can do to help it along:

1. 1.Move the plant to a shady location: While the plant needs some sunlight, too much direct sunlight can be harmful. Moving it to a shadier spot will help protect it from further damage.
2. 2.Water the plant: Sunburn can cause the leaves to lose moisture, so make sure the plant is getting enough water to keep it hydrated.
3. 3.Prune the damaged leaves: If the leaves are severely damaged, it may be best to prune them off. This will help the plant focus its energy on new growth.
4. 4.Provide some extra care: You can also provide some extra care for the plant by fertilizing it with a balanced fertilizer and misting the leaves with water to increase humidity.

Once the plant has had some time to recover, you can gradually introduce it to more sunlight again. Just make sure to monitor it closely to avoid further damage.

And about your zig zag, it sounds like your zig zag plant may be experiencing some root or stem rot, which can cause the stems to become weak and fragile. This can happen due to overwatering or poor drainage, which can lead to fungal or bacterial infections.

To help your plant recover, you should first remove any damaged or rotted stems and leaves. Then, check the soil and make sure it is well-draining and not waterlogged. It may be helpful to repot the plant in fresh, well-draining soil to ensure that it has good drainage. You should also adjust your watering routine to ensure that you are not overwatering the plant.

To propagate the plant, you can take stem cuttings from the healthy parts of the plant and root them in water or moist soil. Make sure to sterilize your cutting tools before taking the cuttings to prevent the spread of any infections.

With proper care and attention, your zig zag plant should recover and thrive!

Good luck!