Are the BDE and BN legal assistance offices only for Commanders, or can soldiers also use them for legal guidance?

I think a distinction is in order.

There are Legal Assistance Offices (LAO) that are usually installation or regional in nature. The offices are there to serve all individuals within that defined scope (i.e., the Army's LAO for Fort Belvoir or the Navy's Region Legal Service Office for for the Naval District of Washington) and are (usually) not service specific.

Unit specific legal assistance could vary based on the service, but for Army units (both AC and RC) that have one or more attorneys assigned to their staff, the commander is required (AR 27-3*, Para 4-1b) to provide legal assistance services for the unit Soldiers depending on the type and number of attorneys as well as available resources (e.g., the 82D Airborne Division's LAO).

Sometimes they are both such as in the case of the XVIII Airborne Corps/Fort Liberty LAO.

If there are inadequate resources, legal assistance can be restricted to "critical functions" and/or limit the use by certain eligible persons such as retirees, active duty dependents, etc.

However, there are certain legal assistance services that are required to be provided to eligible Soldiers if they have requirements that fall into the "must provide" category in areas such as family law (child custody, support, paternity, etc.), estate planning (wills, guardianship, powers of attorney, etc), and so on. Someone MUST provide those services to eligible Soldiers - the unit or some other entity. The full list of what required services are needed in which type of cases is in AR 27-3, section II (paras 3-3 through 3-5).

Without knowing your unit or your location I can only give a general comment. It's very possible that your unit commander has prioritized what legal assistance can be provided from the limited legal assets in the unit to certain functions. However, the command is still responsible to provide (directly or indirectly) those required legal services I mentioned above (again, based on the type of situation).

Have you first checked to see if there is a LAO on your installation? If you can't find an entity that will provide legal assistance to you, then you need to talk with your leadership as it may not be obvious, there is a gap that needs to be addressed, or (possibly) the legal assistance that is supposed to be provided by your unit isn't because someone in that office (or someone that told those individuals) doesn't understand the requirement.
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* AR 27-3 - The Army Legal Assistance Program - https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN8991_AR27-3_Web_FINAL.pdf

Your installation should have a legal assistance office that can provide legal assistance to you (and your family). That is what the office is set up for and is resourced for to do. They are typically located within the JAG office or sometimes within the installation support center.

Judge advocates in the Bde/Bns are thus not normally resourced to provide this type of legal assistance. Bde Commanders (and some Bn Cdrs) usually have an assigned servicing staff judge advocate (JA -- attorney) whose primary mission is to provide commanders with independent legal advice; they are counselors and trusted advisors to commanders, engaging in the most consequential practice of law. Commanders and JAs will almost always refer a Soldier to the legal assistance office that services their installation.