I think the artist was using his full quota of creative licence with this picture...

But it's a nice bit of fun, just the same.

I think you are probably right with your identifications, and the remaining two look like Seaforths and Scots Guards.

The picture seems to be more about sympathetic understanding for the foot-sore men after a stint, rather than precise accuracy, and we all know the feelings the poor men seem to be showing. I like to think 'Get your feet up, lads, we've got a brew on...' is what they're waiting to hear, along with 'excused further duties' for the rest of the day.