Intriguing trees

Another sharp frost lies on the grass outside all crisp and white and the pond is frozen again; Winter has not yet let up its grip. Today is the beginning of an exciting new tree adventure which I will write all about soon. For now I'd like to share some intriguing trees with you I discovered a few days back.

I headed out to the woods and happily followed deer tracks through hazel, birch, oak and beech. I'd jumped back onto the track home when I spied an intriguing oak. And then another. It wasn't that they had co-dominant stems, it was as if they were co-existing stems! One 'tree' had four stems and the other five. The stems seem part of the same tree and yet they are very discrete and some distance from each other. Can someone please tell me what is going on here? Thanks!

This is the 4-stemmer. 

Bottom right pic, you can see the 5-stemmer in the background.

Here is the five-stemmer - what is going on here?!

And here are three bonus extras including a sinusoidal birch growing at 45 degrees and a tiny, stunted hard-done by hawthorn.