That's a so called "composite" transform, a sort of 2 stage process. And this will work using the project tool.
But sometimes, Arc makes some strange guesses as to correct composites.
But as you want this to happen in Postgres...
A quick check of the book (geographic_tansformations.pdf, in the documentation folder of the install), says there is a direct way to go from WGS84 to RGF_1993, it has WKID (I presume this is the same as a SRID) of 1671.
But looking at the parameters for this, they are all 0 (zero). So RGF is already "functionally" equivalent. They are the same.
So you may not have to do anything to your data, to get them to overlay properly.