Is it possible for a spondylolisthesis grade II patient to have sexual intercourse?

Yes. Position may need adjustment, but the condition itself does not prevent intimate relationships.
Yes. Spondylolisthesis on its own does not mean people can't have sex. If there are symptoms associated with the spondylolisthesis, these should be treated so as not to exacerbate them as a result of sexual activity.
Ask a therapist. Many patients who have suffered spinal injury ask this question. There are positions and methods available that would be safe and enjoyable. A good therapist can help you understand what you can and can not do. You and your partner need to be cautious and perhaps creative, but it should work out.