NATIONAL SECURITY <NSIC.O> STAKE ACQUIRED National Security Insurance Co said a group of investors has acquired 226,243 common shares, or a 22.2 pct, interest, for 27.50 dlrs per share. The company said the acquisition of the portion of the shares over a five pct interest is subject to approval by the Alabama Department of Insurance. It said the sellers included Atlantic American Corp <AAME.O>, Bankers Fidelity Life Insurance Co and Georgia Casualty Insurance Co.