they will be in risk of getting mold or powder mildew, you should really see if you atleast could get it down under 60%
40-50% is perfect, some even do 30% at the end if they had previous problems or just want to completely avoid any, I find 30% a bit extreme 40-50% is IMO best
keep good air flow/circulation with a fan/ventilation, and consider a de-humidifire