Three billionaires from China’s property and Internet industries are forming an online shopping venture to challenge Alibaba Group Holding Ltd. as it heads toward what may be the biggest initial offering in the US. Wanda, China’s biggest commercial land developer, is joining with Tencent and Baidu to form the 5 billion yuan ($813 million) venture. Wanda will have a 70 percent stake while the other two companies will own 15 percent each, Wanda said in a statement.