Thank you so much, this is super useful! Yes, he’s stayed with my parents before and he absolutely loves it/them. He’s super close to my parents so he’ll be extremely happy! I just hope that returning to a new place won’t be too confusing.
Children can be surprisingly adaptable, it sounds like he will be happy with your parents :) Talk about it as much as possible and maybe get him involved in planning his bedroom so he's excited? :)
We moved last summer and it went surprisingly well. In the lead up to it we showed her pictures of the new house and talked about it lots. We packed a special bag together of toys, teddies and clothes so she had access to those immediately which helped so much. Then on the moving day she went on a day out with our friends and there little one. We moved all the big stuff and got the bedrooms and kitchen unpacked so we could stay that evening and then she had another day out with friends whilst we made it liveable. Has your little one had a sleepover before? Maybe getting him involved in some aspects will help but still having a calm space to stay sounds beneficial and its one less thing for you to think about. Good luck and happy new home :)