1. If your boyfriend completed his federal sentence, then it does not make sense that the US Marshals have a hold on him, unless there is another charge pending. However, if there are no pending charges and the federal sentence was completed, the US Marshals may release the hold without taking him into custody.
2. Regarding the ICE hold: Generally, after a State charge is resolved, the county will notify ICE that the person is available to be picked up. General practice is that ICE is given about three business days to pick up the person. If ICE does not pick him up, he would be released. However, if ICE is in the process of arranging to pick him up, the county may accommodate ICE and hold the person a little longer.
3. It is always advisable, but not necessary to hire an attorney. The attorney may get better response from the jail when he follows up with the matter. Also, if the person is not released, the attorney can obtain a court order to release the person.
If all state charges have been dismissed and he has completed all of his federal sentence then immigration does need to pick him up or the county jail should release him. Double check with the county jail to make sure there is not another reason he is being held. You mention the US Marshal's office. Could he possibly have another federal criminal case coming against him? If the phone call to the jail does not clear up the picture for you contact a local immigration attorney. There are several good ones in Wichita.
This answer is intended to provide general information about the justice system. It does not provide legal advice or create an attorney-client relationship. It does not provide the basis for making decisions about a course of action. Legal advice requires much more communication and information than is possible in this format. Many important considerations and factors need to be investigated and discussed before an attorney could give legal advice about this issue. Before making any decisions about a course of conduct readers are strongly encouraged to contact a lawyer and secure an attorney-client relationship.