Oooh, I love a challenge!
How about something seafood-y to start with, king prawns with garlic and coriander for example, served with a really interesting salad, and a dip or dressing on the side. You can make really nice dips from low-fat yogurt, low-cal mayo and lots of chopped fresh herbs. Or, marie rose sauce made of v low-cal mayo and tomato puree, or you could make prawns spicy and serve with raita of lowfat yogurt and grated cucumber
Then for the main have lean meat such as chicken breasts or pork medallions, grilled: you can make a watercress sauce of fresh watercress and other herbs, chopped finely / blended along with garlic, a few anchovies, capers mixed with low-cal mayo and half-fat creme fraiche.
Serve sweet potatoes or butternut squash instead of rice, pasta or potatoes and roast other veg in the oven such as red peppers, courgettes, aubergines etc.
Afters could be lots of strawberries/raspberries with little meringues and low-fat creme fraiche if people want cream.
I don't know how points work, but this should come out at about 650-700 calories, if you allow the following amounts for dieter (other guests could have larger helpings):
125g King prawns
85g pork (very small helping for person on diet, obviously more for other guests)
100g each of butternut squash, red pepper, green pepper, yellow pepper, courgette, aubergine, roasted with spray on olive oil, garlic and rosemary.
100g strawberries, 100g raspberries, 1 meringue nest, 1 dessertspoonful half-fat creme fraiche
Sauces - .
What do you think?