How many airplanes have eight engines?

Between 1 and 6. Most light aircraft have one prop, while the An-225 has 6 jets.

There is no such large airplane so far and such large ones will be necessary and impossible

At least one(!), the biggest planes have six.

six

All are on, at ilde. The engines are not turned off to help ajust glidslope angle, as well as to maintain the correct airspeed. Because of the possibility of a missed approach, they are not shut down...