Hello and thankyou for approaching DoctorSpring with your query.
I have taken a look at the picture. It looks like your son in law has dislocated his ankle. But it is difficult to say for definite on a picture.
I would advise you, to take him to the Emergency room and get it examined and get an X-RAY to confirm the diagnosis.

Once examined and an X-Ray is taken , the orthopedician will reduce his ankle. This is better down at the earliest.
It is nothing to worry and will treated. But it is better when diagnosed and treated early.

For now you can keep ice packs on his ankle.
Do not massage the site of injury and do take him to the ER.
You can give him an OTC tablet Ibuprofen for the pain.

Feel free to follow up with any query.
Thankyou