Question

Can an equilateral triangle also be isosceles?

Answer 1

Yes; in fact an equilateral triangle must be isosceles.
The definition of an isosceles triangle is that two of its sides have equal lengths; the case where all three sides have equal lengths is not excluded.
The definition of an equilateral triangle is that all three sides are of equal length; therefore any two side are of equal length; and, therefore an equilateral triangle is isosceles.