Wrinkly and squishy lithops are typically a sign that they are overwatered. Lithops are adapted to survive in arid conditions and can easily rot if their soil is consistently moist. It's important to let the soil dry out completely between watering.
To determine if your lithops need water, you can gently press on the top of the soil to feel if it is dry or moist. If the soil is dry, you can give the lithops a thorough watering, allowing the water to soak through the soil and drain out of the pot's bottom. If the soil is moist, it's best to wait until it has completely dried out before watering again.
In terms of the lithops not splitting, it's important to note that lithops have their own schedule and will split when they're ready. It's normal for lithops to go through periods of dormancy where they don't appear to be doing anything. During this time, it's important to continue to monitor their soil moisture and avoid overwatering.
Overall, it's important to give your lithops the proper care they need to thrive. This includes well-draining soil, bright but filtered light, and infrequent watering. With the right care, lithops can live for many years and provide a unique addition to any succulent collection.