Biodiesel cannot have a pH as it is not an aqueous solution. It could have an "Acid Number" which relates to residual caustic in the biodiesel (IIRC). This has not been shown to have any impact on the fuel system unless there is water in the fuel. People who wash the biodiesel should have a very low acid number as most, if not all, caustic will have been removed in the first 2 washes.

SG is the density of the biodiesel (weight compared with water - for the same volume) and has no valuie in determineing the quality of the fuel. It may vary because of the feedstock or if residual methanol is present in the biodiesel. It is of no consequence.

Melting point and conversion are the 2 tests which tell us most about biodiesel.
the first can be done using a fridge/Freezer and a thermometer and the second can be done using 27mL of methanol and 3 mL of the biodiesel.

I hope this helps,
Tony