"doesn't really want to go back after"
Well that is the kicker really. Even if your wife was good enough, and I have serious reservations about that because someone that is genuinely good enough at photography to make a living of it wont be asking their spouse to get help form a forum, a photographic career has very long hours, lots of stress, relatively low pay and difficult working works (loose most of your Saturday at a wedding, or shoot an event in the evening). And there is no paid vacation, holidays, scik leave, pension, bonuses, health benefits, career progression etc.
SO why doesn't she want to go back to work? It would be a much easier path, liekly earn more, has more growth potential and will let her see more of her children.
If you want to maximize profit, get your wife back in to full time work ASAP and spend your free time shooting weddings. Weddings are about the only area you can make real money. For about 4 years I was shooting some events in the evenings, but that was almost entirely for fun and to make me feel less guilty about 1the 12Ks worth of equipment I had. I also used to sell micro and macro stock, but that is the most saturated market there is and the ship sailed for that about 15 years ago.
I am an avid photographer and would love to ditch my career and make a living form photography. I can tell you the absolute best way for me, and I did some fairly detailed business modeling, was to ignore the photography side itslef but run wildlife viewing and photography tours out of somewhere like Jackson Hole Wyoming. Take a load of rich tourists around on a minibus to the most likely locations, they pay a few hundred bucks for 3-4 hours. On the side you rent out equipment. No one likes going to these destinations with big lenses, and many don't own one, there are online rental places but many would prefer to pay $200 for a 500mm lens rented in person form you as they pay $400 a day for you to cart them about the place. A good destination has year round tourists. I just don't know a good European destination where this would work as well as Jackson Hole.
Also, if you build up a reputation then being a photographic travel guide can pay. Some of my favorite pro togs run these, they set you back about $5-8K for 10 days but includes accommodation. you would need to know the destination intimately.
But shooting babies and protraits, just not a good idea unless you are already such a well known photographer that it is already paying a living. Your wife is much betetr off going back to work and then go on photographic holidays