If you can find any nutritional info you can plan to eat just that. Put a list on your phone or take a small note in your pocket and refer to it before you go in.
Put lots of salad and veggies on your plate to make it look like you are eating a lot. If your plate is piled then perhaps it will look
"normal" to your dad and brother and they won't bother you. Eat as much as you want and we all know that you won't overindulge on vegetables so don't worry.
Salmon, if cooked well can be mashed with your fork and then chopped up with the edge of your fork or a knife, hopefully enough that you can nibble on it and not get sick. Or perhaps they might have another softer baked fish if you can eat that. Does the salad bar have boiled eggs and do you eat them? If not be honest if anyone says anything and tell them that meat makes you physically sick if not ground and the restaurant has nothing for you to eat. It used to embarrass me not being to be able to eat breads when everyone else was diving in and asking that croutons be left off my salad but I realized finally that being honest was easier in the long run and actually didn't make me seem as dramatic as trying to come up with excuses or becoming sick.
If everyone sits around after dinner with dessert and coffee, try to find cheesecake. Nibble at it in a few small bites to equal two normal bites and drink lots of coffee (take some twin if the buffet place doesn't have it). Maybe talk to Ray before you get there to swipe bites from your dessert or ask for a taste, getting rid of a good bit of it in a way that won't cause concern from others. If you have chosen carefully two bites of cheesecake without the crust should keep you below 50 grams of carbs and that should keep you in ketosis now that you have been on plan for a while if you go right back on plan the next day. Making it look like you take several bites will probably fool your dad and Paul into thinking you are eating as will eating lots of on plan veggies.
It's funny how those that love us want what is best for us but they just don't want us to change even when that is what is best for us. And it's funny how we go against what we know is right to appease those we love. You can manage this Krista, just come up with a plan and stick to it. Make it look as normal as possible and try not to talk about it. Skinny people eat buffets and stay skinny. We can be different for one night and act like a skinny person. We don't have to eat everything because it is there or because we paid for it.