I hope this message finds you well, present circumstances excluded. First of all, bless you for taking on the foster children and working so diligently on their behalf. Second, this is a tough issue because you are essentially at the mercy of the foster system and the court system to which your case is assigned.
As such, there are really only a few options available to you. The first thing to look into would be to file a motion for emergency hearing before the court to expedite your hearing up from the two month setting. In the motion, you would need to particularly point out the wellbeing of the children and the lack of action by the foster system to place them with a cousin in the meantime. I have seen motions predicated on the wellbeing of the child be successful in the past. If you can afford representation, I would recommend hiring an attorney to handle this for you if possible. There may be some pro bono (free) legal services available to assist as well. (take a look at the California Bar Association website to inquire about these services in your area).
Another avenue to explore in at least getting the children to the cousin would be to contact your local and federal representatives to lodge a complaint. They may be able to make a call, or someone in their office may be able to make a call, and get things moving in a positive direction. You may want to attempt to contact these representatives by certified letter with a return receipt. They tend to take things more seriously when they arrive by letter in my experience. They may even have a website with the ability to submit inquiries such as this dedicated to them.
In short, you are getting caught in the government wash, but you are being proactive. I encourage you to remain proactive in your efforts and good things will come.
Let me know if you have any additional questions or comments.
Best wishes going forward!