There is no such thing as 'too many credit cards' as far as credit scoring formulas are concerned. As long as you pay your bills on time and use only a small portion of your available credit limits, you can have lots of cards and great scores.
But if you transfer the properties to your children during your lifetime, they will also get your tax basis in the properties. That means if they sell, they'll owe taxes on the appreciation that's occurred since you bought the real estate