Yeah, that's that fake, two-faced, bipolar, crazy stereotype. We just misundastood

We are two sided in that our energy is naturally scattered aka all over the place. We are the quintessential air sign. The first air sign. So, it basically means we are able to see both sides of a situation which makes it hard for us to pick sides or make a decision. Because of our scattered brains, we tend to give answers that arent thought out, so in that moment we might say one thing, but change our minds or mean something different later. So we get called liars, when we don't actually mean to lie, it's just not the whole truth.
Ex: You can ask me if I like Melissa. I might say "yeah, she's cool", but you might catch me saying how annoying Melissa is and how I hate when she does xyz. Doesn't mean I dont like Melissa, I can get along with her. She just bothers me sometimes. Geminis live in the moment generally, so its also hard for us to hold on to grudges.
Also, we're flighty, we hate being bored and if we do get bored or something doesn't interest us anymore we can be quick to move on to the next thing, which is why we also have the stereotype of being unfaithful in relationships, which isnt always true. (There are a lot of other factors) It also means we dont finish a lot of things that we start.
@emerald you got twin geminis, so it's gonna be like having 4 kids. Gemini is the sign of communication, wordplay and writing, so give your girls tons of books, journals, and eventually cell phones and internet access.