alternatives to holiday alone with dog

I'm posting on behalf of my brother who is thought to have sotos syndrome - which (whilst not formally diagnosed) appears to have similar impact as high functioning autism.

He also has mobility issues, but can with a back support and pain killers, walk a reasonable distance on accessible paths.

He has a dog.

His interests include his dog, technology, card and board games.

My brother is mid 50's.

For many he years he took my parents on holiday, but our Dad has passed and Mum (he is Mum's carer) is no longer able to go on holiday.

This year he will holiday with us for a week, and then will have a week on his own in North Wales (this will be the first time he has a week on his own), but next year due to our holidays clashing with his favoured times, he may have two weeks on his own with the dog.

He likes to be near accessible beaches for the dog.

I'm wondering if there are any options for him to meet similar people with a view to going on holiday with them, or meeting up with people whilst on holiday.

He lives in north east London.

I asked his permission to post this.

Thanks

Jackie