What are they doing to run up the bills? Would it seem unreasonable to an ordinary, non-mustachian?
For example, if you used to keep the heat at 55 during the day and 47 at night, and they "INSIST" on it being 65 during the day and 62 at night, I think you should split the bills equally. If you used to only take showers together for 5 minutes max every other day, reuse the bucket of water for dishes, and then for flushing the toilet once a day and now they each take a 10 minute shower and flushing every time. Yes, you'd be subsidizing them this way, but you'd probably enjoy wearing 2 layers instead of gloves, socks, a hat, and a coat in the house, and they aren't being unreasonable.
I think, assuming you were being relatively reasonable if frugal before, you could expect water, electric, and gas to almost double (though whichever is heating the house wouldn't fully double.)
How long have they been there? 2-4 months? It sounds like you were "helping out" to let them stay with you. I'd say to have a house meeting and say you were glad to help, but the additional household expenses have been more than you thought. Now that they've had a chance to get settled, and save some money, you'd like to talk about "house rules" and rent going forward. Rent should be split 4 ways, Utilities 4 ways, there should be an agreement about day and night temperatures, and the issues you see. Also be open to hearing their complaints or concerns. Maybe discuss chores/ clean up, fridge and freezer space/food issues, yard work, or anything else. If you can't all come to a fair agreement they can keep paying the current rent for November, and be out by December 1.