You can ask for your own room, if possible. Another option, if you are at a hotel, is to say you want to exercise and held to the gym. There you can do your yoga.
As far as meditations, you can breath in energy and use this for both empowerment, cleaning, and protection. If you go out, tell them you want to lay outside in the Sun, and this will help the process. You will want to keep your power up, as you may feel a power drop from stopping yoga.
Pranayama will also be helpful to you. There is a breathing exercise for every chakra. This will give you some physical benefit, plus it is quiet and can be done in the bathroom or something. Alternate nostril breathing will help with balance, similar to hatha yoga, whereas the breath of fire will help with replacing an aspect of kundalini yoga.
Try to stay up a little later than everyone, and that will give time to do a decent amount of work. Unfortunately, I am not sure if you can salvage any workings that you may be doing. That is the pain of these family holidays. Personally, I have stopped taking part in these multi-day trips, whether through friends or family.