I don't understand..are they crated at night also? And if so how do they have access to the yard?

Yes they are crated at night when I go to bed and they do have full access to the yard.

How can they be crated AND have access to the yard at the same time?

They are crated all day and all night too?

I have IRIS Plastic Puppy and Dog Pet Playpen. The
opening is to a pet door going outside. When in the pen they have full
access to the back yard. Is something else I should do to help them
potty train or am I just not being patient enough.

Are they both neutered/spayed? Have you actually worked on training them to go outdoors to go to the bathroom? I really wouldn't expect these small dogs to go outdoors at night by themselves, especially when it's cold, since they have learned that it's ok to go inside. I assume they're using pads during the day?

If you're not up to spending time training them, I would do as mamapinky suggested earlier and put down potty pads at night, but I would also close off access to the outside during the night.

Be sure not to punish them when they have an accident in the house but instead keep them in sight so you can monitor when they need to go. The fact they're having accidents out of your sight suggests they're fearful of what may follow. Try to take them on a long walks after you get home from work and also take them out to do their business before bedtime.