DH and I are in a family whatsapp with my in-laws. Theres currently a 'heated discussion' between BIL1 and MIL. MIL (has form for being extremely unreasonable) is insisting BIL1 visits her sister with her at the weekend. BIL1 has refused (work committments). MIL then trots out 'How would you see if your adult son didnt visit your siblings??'. I'm due to take DN (BIL's son) out soon. BIL1 responds, 'I wouldn't care, unfortunately in the case of Chip it can't be helped'!!!!!
To add insult, BIL2 'replies' to this comment with a crying with laughter emoji, and then adds 'At least BIL1 isnt as rude as (my) DH'
They continue bickering, then FIL messages, 'lets not fight' and everyone goes silent.
They all have form for being overdramatic, petty and rude twats but I really don't want to let this one slide. What can I respond with?