3 simple words
'No, Thank you' is all that is needed. If you are worried that, if they bring alcohol to your home, you will be tempted to drink then meet them somewhere and spend your time doing some other activity. You have been really wanting to go bowling haven't you? or play mini-golf or take a long walk in a lake side park or, or, or....
I promise you that it won't be that big of a deal.
Good Luck!