Oh of course if coffee or lunch can be organized and you want all of you to be friends, sure. To me, a group meeting like that does imply that there is a desire (and possibly a bit of pressure) for all three of you to be friends. A quick note or a hello simply says, "I'm here, this is who I am," and then everyone can decide if they want to progress to "group buddies." When online, meeting as a couple tends to be a bit harder as well, so I still think a note of hello is a very nice gesture.
And please please please don't take this the wrong way, it is not meant as a jab or an insult (I'm simply not sure how to word this any onther way), but you're way more paranoid about people saying hello to you than I am I guess. J always takes the time to tell me about who he's met in the course of his day, who he's going to lunch or coffee or whatever with, so I never worry about being out of the loop. I still do appreciate, however, when these gals take time to acknowledge me. My "weird" alarm tends to start beeping when I feel ignored or avoided.