First, congratulations! It is so important for us to have our unique, independent spaces, especially when married and raising a family! So this is wonderful for you and your family!
As you intuited, sunlight is extremely important for good feng shui. Books talk about windows and "views", but I am really surprised that you haven't read about sunlight. Muy importante!
So, my suggestions are the following:
Paint - Perhaps paint your living room in a yellow to mimic the sun. However, yellows can be a really tough color to get the right one. I wouldn't use bright yellow - it could be overpowering. Try a muted tone. In fact, yellow will appear a shade darker on the walls than it looks in the paint can, so try one shade lighter than the one you pick. And yellow needs some balance so you can pair it with a soft, warm white on the trim and doors.
Mirrors - Use mirrors to reflect and amplify the natural light that you do get. Mirrors can act as another window!
Plants - Live plants will bring wonderful vital energy to your new home! Here are some great suggestions for plants that will remove toxins from your home and some do not need much direct light:
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Clearing & Blessing - Before you move in, or immediately after, open all the windows and walk around your home with a smudge stick (sage) with the intent to clear out the energy left from previous residents. Imagine their energy going out the windows with the smoke. And then place your blessing on the home - it could be a prayer or prayerful request to bring in the most positive energy in every area of your life - health, family, children, career, abundance, etc. Another great way to clear your space is with sound. Read more here:
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And, even more than most homes, DO NOT let the clutter build up! Make sure that you maintain a sense of peace and relaxation and your new home will be a magnificent sanctuary for your new family to enjoy!
Best of luck,