Love Horsfields, such characters. Mine are similar sizes but I keep them outside and they are asleep now naturally outside. I hibernated since they were born so if I equate that to yours them your plan is a good one but if they are indoors central heating will dry them out also despite turning the lights off - so make sure you bathe. I am wondering when their last meal was as you need to set your plan against that otherwise 4 weeks is too long without lights if not hibernating til later and haven't fed / food passed through. But make sure bathe them and put them somewhere at least 5 or 6 degrees for around two, maybe three months and check monthly -even weight them again to check for any excretion / weight loss. Hope helps. I fridge that's fine but check on them. Personally I think tortoises in hibernation lets them recharge their batteries. Once chemical reactions starts on waking them don't rehibernate them again unless exceptional circumstance.