The brutal reality is that a business owner can do what the hell he/she wants.
He/she hired you to build their dream and because you aren’t doing that for yourself, you put yourself at their disposal and accepted their offer in the first place.
Why should they accommodate their staff? That would be like the tail wagging the dog, but all good managers consider the feelings of those who are assisting them in achieving their goals. Maybe your boss hates his job and the business and just can’t be bothered to consider anyone but himself. If he feels like that, the business will eventually fail.
Getting time off work in summer holidays is always difficult. I can remember the bad feeling that arose between me and a team leader. He had no kids and had been trying with his wife for years. He deliberately **** up my chances of a holiday and my wife said she would go with the kids without me. This started a rift with my wife, so the whole situation sucks.
If you want freedom to take time off, start your own business. Hopefully you will make enough money and have the flexibility you desire. From personal experience, I ca tell you that earning a crust whilst standing on your own two feet is very much harder than getting a pay cheque at the end of every month.
If you like the regular money that permanent employment brings, you should switch employers, but expect a different or similar flavour of shit from them too.
I wish you luck in whatever happens.