Q: Are fake lashes and fake nails allowed or not, like fake hair extension (wig)?
A: We have not come across this. If this is in any way resembling the styles of the kuffaar you should avoid it. By the same token, if water is not going to reach where it needs to reach in ghusl and wudhu then it will not be allowed at all.
And Allah Ta’ala (الله تعالى) knows best.
Mufti Ebrahim Salejee (Isipingo Beach)