Cats meows at night because they want attention. Well, cats are nocturnal, so they are more active at night. Also they will meow when you aren’t there to tend them. If they are older and less agile, then it’s easier for them to call for you rather than looking and walking to you. Younger cats would similarly “cry” may be due to boredom or just anxiety being in a new home. Now the problem comes when the meows become a habit. Cats can be pretty cunning and clever, quick to learn what benefit them the most. If the cats learn that you will run up to them when they call for distress, they might make it into a habit (they are very clever). Need more water? Meow for a while. Need some playmates? Meow again. You might end up getting trained by the cats! Try not to reinforce this behavior as much as it pains you.
Now you may understand why do cats meow at night, you may use following tips to code with:
Establish a routine for them, they are a creature of habits and routine, feed her at the same time every day. They will learn your behavior too, if you feed them directly after you wake up, they might link it to means that you feed them whenever you wake up from the bed. In this case, do your own things first for a few minutes, then feed them. If they are bored, then leave some toys lying around for them to mess with at night. For some reason, cats really enjoy boxes as the internet has proven, so throw that in for their entertainment as well, you might find sound of sliding boxes more bearable.
Lastly, ignore them if they meow at you. They need to learn that crying for you does not get them anywhere. Don’t even look at them when they meow, just ignore it and mind your own business. Soon they will learn that it doesn’t work to get your attention anymore (and went ahead to scratch the door or something to get some reaction, if that happens, continue to ignore them). So give them a routine, teach them by letting them learn that meows will not reward them and give them something to do at night. Hopefully, they will stop.