Four tenants in common. Three of the owners died intestate. Does the fourth owner have full rights or, will the children of the deceased partial own

If it's a true tenancy in common, which is likely given the number of owners, on the death of a co-owner his or her share does not pass to the remaining owners but passes to the deceased person's heirs.  If there is a will, it would control who those heirs would be.  If there was no will - i.e. intestacy - the share passes to the heirs at law, which would include the deceased's children.