I don't know if the garages are part of the units or if they are limited common elements. If they are limited then it will be associations responsibility. If they belong to the units, then it will be the units responsibility. A simple check of your condo docs should tell you what they are.
In the event it is the responsibility of the individual units, the HOA can certainly compel owners to do the work, in the interest of safety. Your By-laws will spell out the type and manner of authority given. In matters of safety to other units, NJ law allows the HOA to enter and do the work themselves and apply the bill to the units maintenance account, if they refuse to do it themselves and in a timely manner.
Regardless of who is responsible for the work, NJ law requires that HOA's maintain fire insurance on all "structural" portions. If one of the garage walls is load bearing, it needs to be covered under the HOA policy.
N.J.S.A. 46:8B-14 Responsibilities of association
The association, acting through its officers or governing board, shall be responsible for the performance of the following duties, the costs of which shall be common expenses:
(d) The maintenance of insurance against loss by fire or other casualties normally covered under broad-form fire and extended coverage insurance policies as written in this State, covering all common elements and all structural portions of the condominium property and the application of the proceeds of any such insurance to restoration of such common elements
and structural portions if such restoration shall otherwise be required under the provisions of this act or the master deed or bylaws.
As for liabilities and such, contact your insurer.
Good luck.