It is perfectly normal to be friends with the ex wife.
My friend is divorced but it hasn't changed her relationship with her ILs, they have a long history because she met them aged 16 yrs. she has just been on holiday with her ex SIL. You don't just wipe it all out because there is a new wife. She makes her own relationships. There will be baggage. You are quite right in that if counselling is needed it should not be from you. It is hard to just stand by and not interfere - but it is the best advice.
This would under normal circumstances be headline news


