My older son is nearly 4 and younger will be 1 in a few days. My older son goes through ups and downs with his sibling - finds sharing toys and space hard but is trying hard and we are reinforcing with lots of positive messages and reminding calmly what’s right and wrong. Thankfully he has calmed down being so physical with him (as he never did that to friends or other children and it was a shock to see him headbutt and push, pinch etc). What I find the hardest though is his negativity when around my parents with his younger brother. They are very local and he loves spending time with them when we are not around. If we go as a 3 after about an hour the novelty wears off and he can be very very hostile towards my parents. It was awful when the baby was first born but is still very present. He tenses up and says go away and is very cutting with his words. It’s really getting me down as we don’t go there as often now and I had a very hard holiday away with his brother and my parents. I try to be very positive and calm with him and we do lots of 1-1 time when possible and talk about emotions and how he’s feeling. I’m don’t know where to go with this. He is angry and I don’t know how to help him.  
Hi, I understand that this is a difficult situation. Children tend to have short attention spans and tire with things easily, it's not surprising that, after a few hours, he wants to do something different. To him, a few hours can seem like a lifetime. Children also tend to be more blunt with their words as they're yet to learn tact, it's simply something that comes with time and understanding. Perhaps you could tell him how long you plan to be somewhere or do something. If you're worried about his behaviour, then we suggest discussing it with your GP. You may find it helpful to read our articles on challenging behaviour. If you feel you need further support please e-mail us at askus@familylives.org.uk or call our freephone helpline on 0808 800 2222.
Have you read "Siblings Without Rivalry"? If NO - that might be the best start for you. All kids want to be heard and understood; not shut down when they show an emotion.
While you can't act with out consequences this book teaches acknowledgement. My kids get along really well, at least I don't have too many complaints. 3 of my boys shared a really small bedroom, when the youngest one slept in a pack-n-play