Borders are open and they can cross without any visa. Russia is spreading some fake news about closed borders. There is a list of reception points in Poland (some are walking distance from the border) in case they have problems with finding accommodation:

https://www.gov.pl/web/udsc/ukraina-en (English)

https://www.gov.pl/web/udsc/ukraina---ua (Ukrainian)

[edit] looks like Ukraine doesn't allow men aged 18-60 to leave the country: https://espreso-tv.translate.goog/cholovikam-gromadyanam-ukr...