Son rejecting other family members

Background: Son turned 3 two months ago. He was a bit slow picking up language, perhaps due to learning 2 languages at once, but for the past 6 months or so had a vocab explosion... and got quite opinionated with it lol.

So. A couple of weeks ago, MIL visited (she only comes about twice a year) while son was at daycare, and was still here when son came home. He had an absolute meltdown, would not talk or go near her, she was understandably hurt. I put it down to it being unexpected for him, and also she tends to get in his face a bit and wouldn't step back when I asked her so... eh, annoying but understandable.

Since then, he has been very vocal about not allowing anyone in our house, and not wanting to go in other people's houses (daycare, shops etc are totally fine). A builder came around a few days ago to measure our windows and he almost melted down again and kept saying "No thank you! Shut the door!" (His way of saying "send that person away").

I'm sure its just a phase. But the problem is, we're visiting my family in my home country next week, for only the 2nd time in his life. I've explained to him what will happen and that we'll stay with nanny and grandad, and he just keeps saying "no thank you. Bye bye nanny". I printed off pictures of my family members to try and teach him his cousins' names and recognise their faces, but again he keeps saying no thank you and bye bye.

I'll keep trying with that, and we're going to do a FaceTime before the trip too. Does anyone else have tips for this kind of situation? It's a 12 hr flight and I know we'll all be cranky anyway, but I'd love to make this situation as easy as possible for us all, especially him. We get so little time with my family I really want it to be a good experience :(