I'd agree with keeping the whole thing gf to minimise cross contamination.
There are lots of things you can do that are easily adaptable to gf and the rest of the dinner party won't mind.
eg
Starter: Home made soup using gf stock
Main: Lasagne, using gf lasagne sheets, plus either salad or veg
Dessert: Home made cheesecake, using gf biscuits for the base
All three are simple to make and you can get all the gf elements from any supermarket.
Do check about the lactose thing first though. My ds is ok with small amounts of dairy generally, but couldn't cope with both the cheese sauce and the cheesecake.
Other good gf mains are risotto or paella, as long as you use gf stock either are fine and you can choose whatever 'flavours' you like in terms of meat/veg.
Finally, if you go for a straight forward meat and veg type meal and want to provide gravy, you will need to make your own from scratch using gf stock and either cornflour (check it's gf) or gf flour to thicken. Packet gf gravy is beyond vile.
An alternative dessert that my ds loves is Eton Mess, naturally gf and usually popular with everyone.