Aside from food and water, a major requirement of chicks is temperature. The optimal temperature for chicks changes with their age and must be monitored and adjusted for the first five to seven weeks.
You should make sure that your chicks have around 95°F (35°C) during their first week. The temperature can be reduced by 5°F weekly until they are ready to leave the brooder.
An advantage of using multiple lamps is that if one gets faulty at night (or when you are not available), your chicks can make use of the other until you fix it.
Whether you are using lamps or not, you should always use thick bedding in the brooder that the chicks can burrow into.
If your chicks are huddling together in one location, it is likely they are cold. However, they could also be huddling because they are scared of something, so you should not just conclude that they are cold then increase the heat.