Student bills over the summer

My tenancy for my student house has started at the start of July and it’s a house of 7. 2 of these people have moved in and the other 5 of us are not moving in until September.
The 2 who have moved in have not only been really useless at sorting bills and opening the post but believe we should split the bills evenly because there is a baseline energy charge (standing charge and cost of fridges and freezer etc) but I just don’t see that as very fair that they are only paying the 2/7 of the bills for energy they are using. I am paying bills at home and really cannot afford to pay bills for a house I am not in.

I can see both sides as there is a base energy cost but 5 of us aren’t there and it’s almost impossible to work out the complete base cost. Apart from just splitting the standing charge total by 7 and the 2 living there paying the rest, anyone have any ideas how to combat this??

Secondary issue - they are refusing to sort out water because they did electric (after pestering from the energy company), I can do it but I do not have enough money in an account to be able to have a direct debit come out? Surely as water is by usage, it makes sense for one of their bank accounts to be connected.

Anyone have an ideas?