Interpreting Zero sequence impedance of YNyn0 Transformer
If the Z3 component is very large, like would be found in a 5-leg core or shell-type unit, use Z12 and ignore Z3.
If Z3 is low enough to affect your calculations, like in a 3-leg core design, implement it as a Ynyn0d 3-winding transformer in DIGSILENT PowerFactory.  Use the standard pi-to-tee equations to calculate the effective zero sequence impedances Z0ps, Z0pt, Z0st for entry in PF.