Hi, I wouldn't cancel going, you just need to be really strict with yourself, could you take a box of cereal bars for your breakfasts? or ask if you could have a scrambled egg with no butter for breakfast ,or poached egg and some tomatoes/beans depending how many cals your on you could have a slice of toast or two with that which would fill you up, I would think b&b's can accomodate you fairly well with eggs being cooked a certain way, or maybe stick to fruit and yogurt if that's on offer? if they have continental type brekkies I would stay away from hash browns! they always look really greasy I think from looking in the past quite high in cals, stick to things that wont have been cooked in fat or have any added fat you should be ok then
If your eating out try to stick to chicken or fish, fish is fairly low in calories its just what you add to it that makes it fattening, so don't go for creamy/buttery sauces try tomato based sauces, or if you want a creamy sauce ask for it on the side so you can control the cals a bit more, if you go for pizza or something get a thin crust one and share it with your partner (me and my bf used to get our own when we ate out, well before I was calorie counting lol) so you could half a pizza and get a side salad with it? some pizza places do 'healthy pizzas' now which are smaller and thinner etc with less cheese on.
Will you be staying at your Oh's twins house? you could either offer to cook, or ask them to keep the calories low on yours and don't add butter or cream to mash/ don't add butter to any veg etc depending on what your eating, its easy to dish up yours before they add any butter or other added fats to things, that's what i do with my bf when i'm doing new potatoes i dish up mine then add butter to his.
for lunches I would stay away from baguettes they are really high in calories! maybe jacket potatoes, warm salads (just watch the dressings as these are sometimes extremely calorific!) you could take your own bottle of dressing with you should you end up eating salads? if they have a weatherspoons that's a good option as all the cals are on the menu, their chilli is good, i think the veggie chilli is lower in cals than the meat one too and be nice and warming on cold days.
Hope that helps a little, its really hard when your away as I know how easily temptation can creep in, iv'e gone away to hotels etc before and taken cereal bars with me etc but i see the continental breakfast and the cereal bars go out the window lol so its all about self control and will power! hope you have a fab time on all your weekends away!