Firstly, really well done on losing the 10kg! To answer your questions:
1 - yes, if your DH has been eating a high fat diet, (which is what you should be doing on a low carb diet) but also adding in the carbs, then this is what will have led to weight gain. Is there any reason he won't just eat what you're eating? Carbs are really not essential! If not, then he could always cook his own food?! I cook stuff for me but add carbs to DH's meals - but he, if anything (bastard!) is underweight, so it works out well for us. I totally get what you mean about not wanting to cook more than one meal, and it's a real pain.
2 - where are you going on holiday? I'm sorry to have to say it, but if you take the 2 weeks off, you will seriously undermine and undo all the good work you've done so far. Being on holiday is always a time to relax and enjoy things, but there's no point doing that if you know that when you get back home you'll be back to the starting point! Can you plan your meals so that you can avoid the carbs? Obviously that's not to say you should avoid things like the odd ice-cream or a gin (or two!), but you do need to be careful. You could use the time as an experiment for how you think you're going to maintain when you've reached your target weight.
Good luck! I know it's not easy.