I can get you on Icelandair to Paris and back for $665 total, using outbound 16th or 18th with return on the 25th. With Icelandair, all flights connect at Keflavik, Iceland. So from Boston, you’re in the air about 5 hours, then about 1.5 hour layover in the airport, stretch legs, pick up duty-frees, etc. then board for Paris and you’re there in another 3.5 hour or so. It’s a nice way to break up the trip. Icelandair fly only B757s so the 3 of you together would make a row (there are 3 seats on each side of the aisle).

This is a base fare of $557 and the rest is tax and fees. The base fare is including somewhere between $130 and $165 in fuel surcharges (depending on airline, but typical for transatlantic flights from northeast North America). That means before fuel surcharges, you’re really looking at a fare of about $400rt. That’s not bad, but Icelandair have gone as low as $250rt + all the taxes and fees in recent years. However, it could go up as much, too, since this margin is slim, and past sales are no guarantee of future repeats.

www.icelandair.com

I saw, from Boston, going to Zurich and returning from Munich, on Swiss for $682 total.

I see Boston to Dublin for $519 total on AA.

Icelandair, open-jaw into LHR and out of CDG, for $686.

I know you didn’t ask for these, but you seem to be considering a wide range of options.
 
Another option that does meet your Italy desire, is $857 for BOS-FCO (Rome) on Iberia. I think you could probably open-jaw this with Bologna.