Anyone aged 18 or above can be an executor of your will. There’s no rule against people named in your will as beneficiaries being your executors. In fact, this is very common.
Many people choose their spouse or civil partner, or their children, to be an executor.
Up to four executors can act at a time, but they all have to act jointly. So it might not be practical to appoint that many people.
It’s a good idea, though, to choose two executors in case one of them dies before you do.
Many people choose a professional executor such as a solicitor to act for them but charges can be quite steep. It is helpful to have someone involved with specialist knowledge but your executors can always appoint professionals at the time to help them if they need it - which may be more cost effective.
You can appoint substitute executors to cover the situation if your first choice dies before you.