  Magnetic fields influence the formation and evolution of stars and impact the
observed stellar properties. Ap stars (magnetic A-type stars) are a prime
example of this. Access to precise and accurate determinations of their stellar
fundamental properties, such as masses and ages, is crucial to understand the
origin and evolution of fossil magnetic fields. We propose using the radii and
luminosities determined from interferometric measurements, in addition to
seismic constraints when available, to infer fundamental properties of 14 Ap
stars pr\'eviously characterised. We used a grid-based modelling approach,
employing stellar models computed with the \textsc{cestam} stellar evolution
code, and the parameter search performed with the \textsc{aims} optimisation
method. The stellar model grid was built using a wide range of initial helium
abundances and metallicities in order to avoid any bias originating from the
initial chemical composition. The large frequency separations ($\Delta\nu$) of
HR\,1217 (HD\,24712) and $\alpha$~Cir (HD\,128898), two rapidly oscillating Ap
stars of the sample, were used as seismic constraints. We inferred the
fundamental properties of the 14 stars in the sample. The overall results are
consistent within $1\sigma$ with previous studies, however, the stellar masses
inferred in this study are higher. This trend likely originates from the
broader range of chemical compositions considered in this work. We show that
the use of $\Delta\nu$ in the modelling significantly improves our inferences,
allowing us to set reasonable constraints on the initial metallicity which is,
otherwise, unconstrained. This gives an indication of the efficiency of atomic
diffusion in the atmospheres of roAp stars and opens the possibility of
characterising the transport of chemical elements in their interiors.
