Rude People ruin get together

My sister and her husband are ALWAYS late for family get together dinners. We know they will be even though we plan early so people can visit and catch up. They live next door to us too! Haha! When we assign what to bring we always give them dessert. When dinner is ready we eat so it's all fresh and hot. Snooze you lose. When they arrive we invite them to make up plates. It's their choice to be late so we don't let it interfere with our family enjoyment.