An investment group, including members of the Bass family of Fort Worth, lowered its stake in Walt Disney Co. to 20.8% of the common shares outstanding from 23.3% . . . A group led by Oklahoma investor J. A. Frates, which is attempting a hostile takeover of Kaiser Aluminum & Chemical, said it owns 8,906,450 shares, or 20.12%, of Kaiser Aluminum's common stock . . . U.S. Steel Corp. shareholders overwhelmingly approved the company's previously reported acquisition of Texas Oil & Gas for about $3 billion . . . New World Pictures, Los Angeles, said its directors have authorized a 3-for-2 stock split of the company's common and Class A shares . . . Kmart and First Nationwide Savings reported the opening of seven First Nationwide convenience branches in K mart stores in the Sacramento area . . . Apple Computer said it was joining an effort to develop computer communications standards by a group called the Corporation for Open Systems . . . The International Monetary Fund has set an April 15 deadline for Peru to make about $75 million in overdue loan payments to the agency . . . Du Pont said its research and development budget for 1986 will decline about 4% to $1.12 billion from $1.17 billion in 1985.