Jason's physically the largest of his brothers and has most pronounced jawline. But yeah that would be him. Dick has the finest features (Thought this is hard to distinguish normally in the comics, I'm going by comments made by the writers. ( I think the artist took some license to differentiate the four of them.) Adult Tim usually is depicted with a mixture of his older brother's features, namely Jason's larger jawline and Dick's overall finer less harsh facial structure. And Damien is just Damien since he died before he could grow up fully we can only guess that he'd look somewhat like his father.
XD. I just go by color/height/hair style. Tim always kind of has that shaggy hair type of look and is generally in red. And Damian has shorter hair and generally in green/blue. EITHER WAY, they don't look too pleased lol.