Sydney carried out Alex's plan because Sydney was the leader and Sydney was sworn to be loyal to Alex.
Hey, I have a question. What's up, Sydney?  Is something wrong, boss? Nah.  I'm just curious.  I'm supposed to carry out Alex's plan.  But I'm the leader.  So if I'm the leader, why am I not carrying out my own plan?  Why am I sworn to be loyal to Alex? Well, I can't rightly say, boss.  Are you saying you don't wanna carry out Alex's plan? No, I guess for now we'll do it Alex's way, whoever Alex is.  But never forget, I'm the leader.  Okay?  I'M THE LEADER. Ok, boss, no problem.  You're the leader.  Now let's carry out Alex's plan.