They dont sound very friendly to me the way they are being the cause of so much stress for you. You need to be firm and upfront with them. Tell them that its a Group Project and everyone is supposed to put equal effort along with showing mutual respect and consideration. Talk to your professor and make him aware of whats going on. Dont leave out the threatening to kick you out part.
EDIT. Why op needs to do this ? well OP can either let things be how they are and hope for things to sort out own their own or stand their own ground. There is a difference between being rude, demanding and someone who wont let others take advantage of them.
Next time you meet them, talk politely but clear and firm. Stand, sit straight and look in the eyes.Talk to the point and avoid small talk or topics not related to your project. That would show that you are here to work and not make friends and chit chat.
Tell them all what you have done so far in the project and ask them about their progress. Discuss ideas, ask for suggestion and give them your input about their suggestions or ideas. That would show that you are involved.
As a last resort, go to your professor and be honest about the whole situation. Tell your professor about them threatening to kick you out of the group. Discuss what options you have in all this.