He was in Spain working because that’s his job as a photographer.
Because of course there are no newspapers and magazines in the UK for whom he might have worked.
Furthermore they were divorced and he didn’t live with Olga and Dylan anymore because that’s what they and the courts agreed on. His responsibility was to uphold the divorce decree requirements. No more, no less.
You don't know what the terms of any divorce-related agreements or orders were. If you don't consider that parents have an ongoing duty to their children, particularly their disabled children, in circumstances where the resident parent is unable to cope, that's an incredibly narrow view.
Besides, in August even if he had managed to convince authorities it was an essential trip to fly back, he’d have had to isolate for two weeks before he could go to their house anyway. He wasn’t in a realistic position to help personally.
Why just August? Why not at any time from the point when Dylan's school closed? And if he did have to wait two weeks, so what? At least the mother of his child would have the prospect of help reasonably soon.