This may come as a surprise to you but there is no law against nepotism. It may violate some company policies, but all that would do is cause the violating parties to be disciplined. It does not create a legal cause of action.
We do have laws against discrimination based on race and gender. You say you "feel" that may have also contributed to the decision to let you go. But it takes more than feelings to be successful in court. You must be able to articulate a specific basis to support such suspicions. If you think you can, you should write them down and meet with one or more experienced employment law attorneys in your area to get an informed legal opinion.