I think a bbq is a great idea, and soup for a starter works too.

For ease thats what i would be doing a big pot of soup maybe tomato and then roast turkey and or beef with veg and potatoes.
For dessert why dont you ask people to bring a dessert im sure they wouldnt mind.

What about a big taco dinner? You can prepare the taco filling and warm it up just before the guests arrive. You prepare small bowls with different ingredients (cheese, sour cream, avocado, tomatoes, salad, capsicum, carrots, spicy sauce…) and people can just choose what they want. (Also in this case prepare them in advance and keep them in the fridge) You just need to warm up the taco shells for 5 minutes in the oven and you are ready. Not much fuss! Who has problems with milk just doesn’t choose the milk products.
You could then prepare a cake for dessert.

Good on you for hosting Christmas dinner at your place! I am quite sure your guests will be happy to help you out, so why don’t you ask them to bring a dish, they will be understanding of your need to attend to your baby. If you want to plan a menu..BBQ is fine! Always fine! Ask your guests to bring a plate…throw it all together. Easy! If you want some ideas, check out Taste.com.au they have a selection of Christmas dinner menus which you can get ideas from. Don’t be afraid to ask for help. Enjoy your day!