Proof-of-Work (PoW) is the core of the most popular consensus protocol among current mainstream blockchain systems including Bitcoin. Selfish mining attacks are a possible threat towards PoW-based systems and recent works have shown that a miner can profit using selfish mining if it has more than 25% of the overall mining power. In this paper, we present a simulator based on a Markov Process model that can analyze scenarios where there are multiple, independently working selfish miners. In our evaluations, we present detailed results with two attackers showing that the threshold for profitable selfish mining decreases to 21% in this case.