Extent and Limits of Authority
A patriarch can only give blessings to members of his stake and his descendants. In the past, Patriarchs could also give blessings to siblings and, in some cases, family friends. In the event of a language barrier, the patriarch in a neighboring stake can speak the blessing in the language of the one seeking the blessing. Also if a stake lacks a patriarch (as occasionally happens when one moves out or dies suddenly) or likewise, when a blessing is needed in a district, then a neighboring stake's patriarch may serve.
Sometimes there will be more than one stake patriarch.
It is not uncommon to have more than one ordained stake patriarch in a stake, as many are given non-functioning or emeritus status. This can occur as they age, go on missions, or move out of the stake. When a patriarch moves into a different stake, he is to inform his new Stake President, who will decide whether or not to use the patriarch. This can also occur when a stake patriarch is called to an administrative position such as the office of Bishop, though such callings are rarely approved by the Quorum of the Twelve.
Generally, there will be only one functioning stake patriarch. However, if more blessings are being requested than a single patriarch can handle, another functioning patriarch may be called to assist. In such cases, the patriarchs may often be given a geographical area of responsibility within the stake.
There may also be areas were there are a large number of foreign language wards or branches. In such cases, a stake patriarch may be called specifically for the language in that area. He generally would only give blessings in the language he was called for, whereas the original ordained patriarch would give blessings in the predominant language of the area.
Ordination of Stake Patriarchs
Stake patriarchs used to be ordained by the Patriarch to the Church, a member of the First Presidency, or a member of the Quorum of the Twelve. However, due to the growth of the Church, that authority has been delegated to stake presidents. When it is time to ordain a new patriarch, a stake president will submit the man's name to the Quorum of the Twelve for approval. The new stake patriarch, generally, is then sustained at the following stake conference. The retiring patriarch is not released, but is instead given non-functioning status and may be given a vote of appreciation.