This is an interesting question. there are at least two meanings for "大家", one means "we/us", and the other means a well-know person in a field.
so, if "大家" means "we/us", you can't say "大家们", it's not correct, because in this case "大家" has been represented "we/us"; but when you describe a group of people who are well known in a field, such as calligraphers, you can say "大家们", here are the examples
English: The calligraphers from china have been sleeping.
Chinese: 从中国来的书法大家们已经睡觉了。
but most of time we would like to say in chinese as
从中国来的书法家们已经睡觉了。
in most case of chinese, adding the word "们" at the end of a creature may means the group of this kind of creature. "人们" means people, as "人" means human being.
However, it can't be described as a simple question, to understand all about that you may need to know more about china and chinese.