Tips on Wake and Funeral etiquette? Can I attend only one and not the other?

Background information: My son's Grandfather died on Wednesday morning. My son is 22 years old. My ex-wife and I have been on excellent terms for many years and her entire family always liked me very much. We were together for over 6 years. She called me in tears and asked me to wake up my son and break the terrible news to him, about his grandfather. My son was devastated. He was very close to his "Pops". He was, "beside himself", as they say. The next day, my daughter (from my first marriage) and I sent beautiful flower arrangements to my ex-wife and her mother. My ex-wife texted me and thanked me twice and we exchanged some thoughts by text, about her dad.

The family is holding a wake/viewing on Friday and graveside services followed by a big get together at a hall on Saturday. The family is a very large and informal, communal type of family. They have not officially invited anyone to attend, but by word of mouth, they expect to see about 150- 200 people attending.

I have to work every Friday and Saturday. Is it okay to attend just the graveside services and the after event on Saturday, without attending the viewing/wake and memorial service on Friday? Can I just show up, with my daughter, to the graveside services and then bring some food and beverages with us to the after event? I don't want to assume that because I'm very close to my son and I knew his grandfather and the family very well, that I can just do whatever I want.