In terms of Work getting the TR reboots here
TR(2013) already had its Multi-player stuff stripped, and as far as I remember had no achievements, just strip out the SteamAPI call.
RotTR had some stupid Micro-transaction/card based community challenge mechanic, That would have to be removed or altered. They might have already done that, I've not really followed it.
No idea with Shadow of the Tomb Raider, avoided looking at it knowing it wasn't coming to GoG any time soon.
Legend, Underworld and Anniversary were sold DRM free from Square Enix's own digital store (before they pulled them and removed access to the purchased downloads), so they could have been here at any time.
The top down Lara Croft games, I assume they had SteamAPI networked multi-player. So they'll either have to make them Couch Co-op only or do the work to support Galaxy MP, I'd be happy with the former.