Focus discussion on the 'new' type of vaccine this is. It isn't fully tested and doctor's do not understood what the long term effects are. Then focus on the age of the kids (15 and 8) and tell them that it is more risky at that age to have a side effect from the vaccine than a reaction to COVID-19. They are putting the children at more risk by giving them the vaccine.
If that doesn't work punch your BIL in the face and tell him to man up.
Focus discussion on the 'new' type of vaccine this is. It isn't fully tested and doctor's do not understood what the long term effects are. Then focus on the age of the kids (15 and 8) and tell them that it is more risky at that age to have a side effect from the vaccine than a reaction to COVID-19. They are putting the children at more risk by giving them the vaccine.
If that doesn't work punch your BIL in the face and tell him to man up.