I t would appear that he was in the 2nd Battalion of the RDF before transferring to the London regiment as the 6 digit number for his time in the London Regiment was post Jan 1917. The fact that he is shown as wounded whilst with the RDF may explain a transfer after a spell in UK hospital.
This does tie in with the uniform worn in both photos as the RDF photo with its tunic pattern and brass titles would suggest it predates the London one.
The other 2 soldiers in the London photo may not be relations but fellow members of his platoon.
His RDF regtl number was of the same batch as was allocated to other London Regt transferees circa 1915-16 see
https://www.dublin-fusiliers.com/oth...0s/43000s.html so he may have started with the 1/6th Londons moved to RDF (with a new number) and then back to 1/6th after injury (again with a post 1917 number) and it is these numbers that you see on the medal records.