Cherry Trees

Hi. I have two possible beds for putting in cherry trees. One is 12 foot by 4, and the other 15foot by 4.

I want to put in two trees which will pollinate each other. My question is how best to train them. I’m only meant to have trees up to 7 or 8 feet high. On a previous allotment I’ve festooned them and this did work well but they were still getting quite big when I left that plot. I’m wondering if doing fan training would be better and would welcome any thoughts/advice on this please