Akshi - Yes you can.

|Difference of other 2 sides| < Third side < Sum of other 2 sides

Now the 2 sides of isosceles triangle are 5 and 8
So, we can form 2 triangles with sides 5, 5, 8 and 5, 8, 8

Check if both the triangles satisfy the above condition/inequality:

For 5, 5, 8
|5 - 5| < 8 < 5 + 5 [True]
|8 - 5| < 5 < 8 + 5 [True]
Col. A < Col. B

For 5, 8, 8
|8 - 5| < 8 < 8 + 5 [True]
|8 - 8| < 5 < 8 + 8 [True]
Col. A = Col. B

This means both 5 and 8 can be the third side of the isosceles triangle.

Hence, option D