There are often multiple causes of groin pain as it represents lumbopelvic dysfunction, which can place excessive strain on many structures.

Yes the pain with the sit ups is indicative of a "hernia" although that term is fading out. Often Hernia's are actually minor tears in the external oblique, transversus abdominis or rectus abdominus insertions. Due to there being no palpable hernia present it is unlikley surgery will be of benifit for this.

You are also complaining of pain squeezing the knees together, indicative of adductor related groin pain, which would most likely be due to tendinopathy.

Its possible for nerve entrapments to occur around that area too as you mentioned you experience nerve pain.

Commonly adductor and "hernia" pain will refer to the genital region.

My question to you is- Where is the worst pain located? (the one that stops you from continuing activity)