DD1 - Walked at about 19.5 months - she did have hip dysplasia but that was all over and done with by 6 months ish so I don't believe that really impacted it - she just was slower on the physical side of things. She did the knee walking thing you mention your DD2 does for about 6-8 weeks I reckon.

DS2 - Walked at about 14 months - he is a far more physical being than she is. He couldn't stand on his own, he mastered walking before standing still - which is typical of his caution to the wind attitude.