Hi
My lo is 17 months and we have travelled a lot and also done 4, 12 hour flights with him. I found the most important thing is to try and keep things as close to his normal routine as possible and also to be flexible if need be. Its only normal to have family want you to do things their way, believe me, I know, but compromise with them and you could enjoy your holiday, if you fight them then your holiday will just be stressful and you will wish you were home, again I speak from experience.
I also take my lo's teddy and he uses a muslin to help him sleep. He also uses a grobag which helps him feel like he is at home. I use the same routine, dinner, bath, bottle, story then bed. He is usually a bit unsettled for the first few nights but I keep him really active - and on holiday that's easy - and he sleeps like a baby!! When you get home he will probably be unsettled again and I recently posted a message for help with my lo waking all night after our last holiday. It is important to really keep the routine going when you back as we got into the bad habit of letting our lo sleep late after a bad night.
I will be honest its not easy but try and relax and use the fact that you have babysitters to enjoy time with your partner.