The jointly owned CD's will transfer to the surviving joint owner(s) upon the death of one of the owners. Jointly owned assets will transfer outside of the estate and directly to the survivors. Assuming these accounts were owned jointly for more than one year before the date of death, they will be tax based on the percentage ownership of the decedent. For example, if there were only two joint owners, 50% of the value will be inheritance taxable. If there were three joint owners, 33.3% will be subject to inheritance tax. You must also determine who is responsible for paying the tax. If there is a will and there are other probate assets you should check to see if the will holds the estate responsible for paying the tax on ALL taxable assets whether probate or non-probate in nature.
Although Doug's response is generally correct, there is recent case law which may in the appropriate circumstances make the CD's Estate assets instead of the property of the surviving joint tenant. The factual analysis is complicated so it is important that you review the situation with a knowledgeable and experience estate administration attorney.
I suppose, as pointed out by Jay, I should have added the disclaimer that my response above is only generally the case. However, there could be other issues at law in your case that would cause the jointly owned assets to be treated in a way other than their ownership designation would warrant warrant on its face and thus causing them to be added to the probate estate. There is no way for me to make that determination from the facts provided and you should therefore discuss your facts more fully with an experience attorney.