You don't mention lenses. Do you have a few M-mount lenses that you use with the M6 and M3? If so, I would definitely keep one of them, probably the M3.
A first pregnancy is a wonderful opportunity to take lots of pictures of your wife (trust me, on the second, third, fourth, etc., you won't have the quiet time you two have right now). Looking back on the hundreds of pictures I took of my wife when she was pregnant with our first child (taken with an M6-TTL by the way) I wouldn't trade them for anything. It's nice to remember a slower and more peaceful time.
And the M cameras, for me, work much better for those kind of personal, intimate photos. They are so much less intrusive than your DSLR or the Hassy, and so much easier to just grab and shoot when the moment is right. I always kept a roll of Tri-X in the Leica throughout her pregnancy.
Just my 2¢ worth.
Congratulations on the baby on the way.
Best,
-Tim