Myself, I would not force the writing during the summer if he hates to write. If social skills are priority 1, I'd put my focus there, with lots of practice opportunity, debriefings where relevant, and just generally conversation about what's going on in these new experiences.
The writing process includes a lot of cognitive function before the pencil is set to paper. Address the language and social skills issues, as these are a lot of what I see you mentioning with regards to his writing skill. Get the language skills in place independent of writing, and then work to translate.
DS and I will be working on "writing" this summer, but no words will go onto the page. It will be through working on flexible thinking, clarifying meaning and sequencing of thoughts. We'll do this mostly with Story Cubes and reading together.
