Quite a successfull trip!!
Just a follow-up..
Following some advices from here and armed with my 4 DS0087 coupons, I was able to upgrade two of us on the YUL-PHL leg AND the 4 of us on the PHL-LGW leg on the 4th of July!
On the return on the 26th, I didn't had any coupon and the flight was overbooked. After check-in, we went to the gate and waited for the boarding. Few minutes before it, I went to the gate and spoke to an agent, asking him very politely if there was a slight chance of getting an op-up because of the overbooking and if my status *A Gold could help. He asked me how many we were, told him 4, and he said, no luck, I only have one seat left in Envoy. I thanked him for his efforts and went back to my group.
Two minutes later the same agent came to us and said, "I have 4 seats available, two seated together and two others separated. Are you interested?" Wow!! It took us about 2½ seconds before saying YES!!
So, all in all, a very interesting trip and a fabulous journey in Envoy on both legs across the Atlantic.
Thanks to all for their advices!