Whether or not you can keep leopard geckos housed together can be a controversial subject.
Though housing leopard geckos together is a controversial subject, housing multiple male leopard geckos together is not. Most people know not to house male leopard geckos together because of how territorial they can be. Housing them together almost always results in them fighting or stressing each other to the point that one is injured, killed, or both are injured or killed. It is not a risk you want to take.
Each gecko has its own personality. Some female geckos are okay with being housed with others, some are not. Trying to find out if two female leopard geckos are okay together is still risky because even if you are monitoring them, they can suddenly decide they do not like the other female. If this is the case, you need to have an enclosure already bought and set up if the females decide they do not like each other. However, if that is the case and you have two enclosures already set up for them for that event, you may as well separate them anyway.
If by chance your female leopard geckos do get along fine and you want to put them in the same enclosure, there are some things that need to be added and changed as to how the enclosure is set up.
MORE SPACE: A rule of thumb is a 15-20 gallon enclosure for a single gecko which means multiple geckos mean more space. Some say a 30 or 40 gallon enclosure is enough.
MORE HIDES: There is a rule with geckos stating one gecko needs 3 hides (one on the warm side, one on the cool side, one for a humidity). This means you may need to cram 6 hides in to one enclosure.
FOOD MONITORING: If you have multiple geckos in one enclosure you will need to monitor them for food and nutrients intake. If the geckos were separate you would be able to tell when each gecko finishes their food and if they eat it all. However, with multiple geckos you would need to monitor them to make sure one is not bullying the other and eating all the food while the other starves.
WASTE MONITORING: An animal’s waste is a great way to keep track of the health of your animal. With multiple animals in one enclosure it would be difficult to tell which gecko is sick when monitoring their waste. Another issue if one of your geckos is sick and it is contagious, making all of your other geckos sick if the sickness spreads.
Conclusively, male leopard geckos cannot be housed together under any circumstance and females can be housed together but it is not recommended and is more difficult and more risky than housing them separately. See more in the video below.