In this paper, we focus on the interference mitigation problem in two-tier femtocell networks where the femtocell users (FUEs), share the same frequency band with the existing macrocell users (MUEs). More specifically, we formulate the problem as a multiple-leader-multiple-follower non-cooperative hierarchical game to maximize the utilities of both MUEs and FUEs by obtaining the optimal powers. We theoretically prove that there exists a unique Nash equilibrium in the hierarchical game. We then develop a distributed iterative power update strategy to allocate transmission powers efficiently. In addition, we take advantage of dynamic and adaptive pricing and maximum power adaptation to manage the interferences introduced by the transmission powers of FUEs and mitigate the near-far effect in the networks. Furthermore, we propose an admission control algorithm to alleviate the network congestion when the quality of service of FUEs cannot be guaranteed. We carry out extensive simulations to demonstrate that our proposed scheme is able to maximize the utilities of both MUEs and FUEs, while guaranteeing MUEs' required signal-to-interference-plus-noise ratios and admitting as many FUEs as possible to share network resources.