My theory is simple - the DFS will drive the IRR and the decision to invest in the project (and also drive decisions by Offtake partners to get equity for Offtake Agreements and finance agreements in general).
Why GR Engineering, say for example you don't have trust say in Hauyou - just a guess - then you don't want that partner doing the DFS so I suspect they are looking at someone independent to do the inputs to the DFS (and presumably the IRR calculation that goes with it).
Or alternatively, and more likely theory, is your lenders/Offtake potential partners want an independent valuation/feasibility study rather than one done by one of the substantial holders doing that evaluation itself - just a guess.
GR Engineering is actually a reputable company, well known in WA. Here is a list of some of the engineering projects they have actually done/constructed:
https://www.gres.com.au/projects/default.aspx
And this is what you might see in their approach to feasibility studies:
https://www.gres.com.au/services/feasibility-studies.aspx
Based on this link below, there is a reference to this company completing 160 feasibility studies in the past, albeit the complexity and areas of expertise are not documented:
do not advertise external links.au/companies/news/209334/fyi-resources-welcomes-start-to-gr-engineering-led-dfs-due-mid-2019-209334.html
All IMO
