Yanbu to be upset and angry. But please dont take it out on the sign, and please dont do anything that is going to backfire on you, result in any court action or affect your credit rating (like not paying rent, etc)
I suggest you work with the new owners and tell them that you will need time to find somewhere to move to. You will do your best, but cant move until you have found somewhere new you can afford.
If they chose to evict you then, well, the ball is in their court. But you need to communicate with them.
The sale could have happened fast-ish, without many viewings, etc, if the relatives have inherited the house, and one of them is buying the others out. It would then just be a question of having it valued, having a look, and sorting the finances out.
Have you been given a proper, legal section 21 notice? What does your contract say about termination? I think it would be worth speaking to CAB too, and Shelter, about your rights in this situation.