The plant in the first photo is a Dieffenbachia (a.k.a. Dumb Cane); the second is a Dracaena (a.k.a Corn Plant or Dragon Tree). Both like to get somewhat dry between soakings, and both benefit from moderate levels of light. Unless the blinds in the photo were closed just to take the picture, we recommend opening them to give the plant much more light. Aside from normal leaf shedding, where the oldest lower leaves gradually yellow and dry, excessive leaf loss can be due to insufficient light, over- or under-watering, or less often, nutrient deficiencies.
If you are using saucers underneath the pots, make sure they get emptied after the water has drained into them so the soil does not re-absorb the excess and become too saturated. Soils that stay wet for too long don't have enough oxygen for roots to stay healthy. For saucers under heavy pots that can't be emptied into the sink, you can use something like a turkey baster (not one used for food) to suck up and dump the extra water. Over-watering plants is also easier when they are in old potting soil, because it becomes denser and less airy over time. If these plants haven't been repotted in a year or two, it will be good for their root health to remove the old soil and replace it with fresh potting soil.
There is no watering schedule to follow; rather, you need to check the soil by hand before watering, because the plants will dry faster or slower depending on multiple factors (time of year, age, soil quality, indoor temperatures, indoor humidity, stage of growth, and so on). With plants this size, where picking up the pot to judge its moisture weight is impractical, the best way is to feel the soil a finger's depth down and see if it's moist or dry. If that's not possible, a sharpened wooden pencil or skewer (longer than a toothpick) might work, where you can see how damp the wood becomes after a minute or so. (Let the wood dry afterwards and you can use it again and again for this.) Moist soil won't need watering as deeper roots tend to stay wetter, but dry soil could use a soaking. Plants should be watered thoroughly when needed but infrequently enough that they have a chance to dry a bit in between. Frequent, lighter waterings can lead to an imbalanced root system or outright root loss, and surface dryness isn't a good guide to go by. As a rough guide, you can check on them twice a week until you get a sense of how often (in summer) they tend to dry out sufficiently. It is unlikely that pots this size will need soaking more than once a week; possibly even less, but as mentioned earlier, a lot of factors influence this.
These plants appear to be in good health otherwise. Trim off the dead leaves (they may come off on their own with a gentle tug) and, if in doubt, less harm will come to them in the short term if they are under-watered versus over-watered.