I believe the children should not be left out of their Mother's Memorial Service and it will probably come back to haunt the controlling family, i.e. the Paternal side one day.
When my daughter died her twin daughters age 4 were both in attendance, (no casket) just a Memorial her father had given. It was quite large a lot of people in attendance.
The children still today, 2 years later, miss and talk about their mother, from day one when she disappeared from their lives till today, they remember EVERYTHING about her.
They have been to psychologist office for ongoing grief counseling from day one as well.
So, although doing well today, as well as can be expected under the circumstances, and are typical children, not both are the same either.
And they would never forgive had they been left out, I'm sure.
J.