The discovery of radio-quiet, x-ray thermally emitting isolated neutron stars (XINSs) in the ROSAT All-Sky Survey revealed a previously overlooked component of the neutron star population. Advancements in x-ray instrumentation and the availability of deep, wide-area optical surveys now enable us to explore XINSs at fainter x-ray fluxes and greater distances. In this study, we investigated candidates selected from the 4XMM-DR9 catalogue using XMM-Newton, focusing on long-term flux stability, spectral characterisation, and astrometry. By leveraging resources from the XMM2ATHENA project—including updated catalogues, multiwavelength characterisation and machine learning classification—we refined our understanding of this sample of soft x-ray emitters. Our findings enhance the characterisation of XINS candidates, laying the groundwork for more targeted investigations and future catalogue searches.