Witnesses and Beneficiaries

As far as I'm aware, I need two witnesses to making a will, neither of whom can benefit from the will. I believe one of the witnesses can usually be the solicitors secretary.

My parents are legally separated and will be divorced in the near future. My mother is currently living with a partner and may, at some point after the divorce, get remarried. I intend for both parents to be beneficiaries.

My question is, can I have my mothers partner as a witness? He won't be listed in the Will as a beneficiary but, obviously, if they get married, he will benefit just by the fact that my mother is getting half of the estate.

What would happen if a witness pre-deceases you, does that mean you only had one witness, invalidating the will? You cannot be expected to provide for all events in the future. AFAIK it is the status of the person at the time the will is signed that is important, apart from which, in the normal course of events your mother's intended is not an intended beneficiary i.e. he is not mentioned in the will. In the event that your mother predeceases you, he is still not a beneficiary unless you choose to mention him specifically as he is not a blood relation.