If the shares are held in a nominee account, you'll need to contact the platform on which the shares are held. The shares are valued from the date of death of the person who held them.
Executors of the estate (the person/people dealing with the deceased person's estate) have the choice of selling these investments and receiving cash, or transferring the ownership to one or more of the beneficiaries, but only once probate has been granted (for example, when the administration of the deceased person's estate has been sorted).
Paper share certificates are slightly more difficult to sort out and will probably cost more, but if you approach a platform it will probably be able to help you value them and help with the administration.