Ok, well do you know that you will be ovulating around the time when he will be home? Have you been testing with opk or charting your temps?
If he is going to be home for just a couple days, then your window or opportunity is really short. If he has not released in a long time, then the sperm are "over mature" in a sense. They start to die off, and they will not be strong enough to make it to the egg. That is if there will be an egg there waiting.
I wouldnt worry about buying the fertility vitamins for two reasons. One it takes a while for them to get into your system for them to be benificial. Secondly they wont make you end up with twins. They wont make you release more than one egg. They help with your reproductive system as a whole. you would have to take fertility drugs in order for you to be at risk for multiples and you can only get them from a doctor.
**And mega props to your hubby for going up to Northern Cali to fight those fires. I am in the Fire/Rescue Business so I know what its like.