Will

[Unicorn25]

Can anyone who is included in a will contest or can only the beneficiary contest?

Usually it's people who have been left out of a will, or who are not a beneficiary who contest wills.
I guess if a beneficiary felt the share-out was unfair they could raise it with the executor, but they'd probably be on a hiding to nothing if the will is otherwise in order.

Anyone can contest a will, regardless of whether they are a beneficiary. A beneficiary may be able to claim a greater proportion of the estate under the Inheritance Act.