Advice on divorced parents

My parents divorced during the Covid pandemic. They both (already) have new partners and I have no idea how civil they are with each other, let alone their new partners. I’ve been researching over and over, and most sites say that it’s best they politely ignore each other ? My initial thought was to have my dad seated with his partner and her children, and my mum and hers with my siblings, but at the same time I don’t want my dad to feel left out or isolated from his biological children. We’re quite a way off yet (don’t even have a date set) but it’s something I’ve been anxious about since we got engaged. Does anyone have any experience or advice to help with planning, seating arrangements, and keeping the day happy? I know I need to talk to them both but I have no idea how and where to start. Greatly appreciate any input please and thanks in advance ??