We introduce new heuristics of HTN (Hierarchical Task Network) planning for mobile robots with two arms/hands that pick and place objects among movable obstacles. Based on our new heuristics, the robot moves obstacles if necessary, picks and places the target objects without collisions. The robot chooses the (right or left) hand to use for each manipulation in order to avoid collisions and reduce the number of obstacle movements. In most of the previous approaches that combine task planning and motion planning, collisions between an arm and obstacles are checked only by the lower-level geometric motion planner. Therefore, the high-level general-purpose task planner often produces a plan that is not executable by the lower-level modules. On the other hand, in our new heuristics, the task planner roughly checks collisions, and produces executable plans.