Both plants look like different varieties of Peperomia, though we are not certain about the all-green plant because there isn't enough growth left on it to help much with ID. Peperomia are semi-succulent plants, and they are sensitive to being over-watered. Make sure the soil is getting fairly dry to the touch about an inch deep into the container before watering, and if the pot sits on a saucer to catch drained moisture, empty it promptly after watering so that collected water doesn't seep back into the soil, which will keep it too wet. (If the pot does not have any drain hole in the bottom, it would be best to move the plant into a pot that does.) Peperomia do best in moderate light levels (near a sunny window or under grow lights), with moderate humidity levels and just enough watering frequency to avoid getting super dry for very long. They handle getting too dry better than staying too wet. Leaf drop is a common symptom of plant stress, though what causes it can vary considerably depending on the tolerances of the plant and what conditions it is growing in.

Make sure the plants aren't too close to a kitchen with a gas stove, in case the appliance is leaking gas or not burning efficiency, as ethylene can cause plants to shed healthy leaves. If the plants are in the direct path of warm, dry air from an air vent, close to a radiator, or next to a drafty window, those temperature fluctuations might be contributing factors. If there is a pest present (thrips on the foliage or mealybugs on the roots), we can't see them in the photos, but you could inspect the leaf crevices (like where they join the stem) for any damage, and pop the plant out of the pop to assess root health. (Root mealybugs can look like white fuzz clustered around the roots.)

Our main suspect is soil moisture, though, so try letting the plants dry out a bit between waterings, and are placed in good light, and see if new growth appears in the next few weeks. Houseplants don't typically grow as vigorously (or much at all) during winter due to low natural light, but a plant having to replace lost leaves might be more likely to grow a bit. Do not fertilize for now, as too many nutrients in the soil can damage roots.

Miri

Thank you so much. 

You're welcome!