How much is a family ticket to heathrow?

theres one adult and 6 children, 1 who is 16 with a 16+ oyster card. we are going to heathrow to collect our dad and both my parents have oyster cards. i tried going on the websote but it made no sense to me so can any one help me and tell me whats the best deal i can get and how much it will cost. thanks in advance