Can a right triangle also be an isosceles triangle

Yes because a right triangle just needs one angle to be 90 degrees and an isoceles triangle needs two out of the three side lengths to be equal, and both of those qualities are possible to be in one triangle

When we know 2 sides of a triangle,
the third side must be less than the sum of the other 2 sides and
the third side must be longer than the difference of the other 2 sides.
If the 2 sides are 2 and eleven, the third side must be greater than 9 and less than 13.

Source:
http://www.1728.org/trianinq.htm