I have a 14/15 month old and he is a pretty cruisy boy!

He likes playing with blocks, cars and emptying toy boxes by tipping them upside down.
He is not interested in TV however his friend who is 2 weeks younger then him can be glued to the TV for more then 1/2 an hour at a time so I guess it depends on what type of child you have. My DS likes to play with the curtains while we watch TV. Other then that the only time he sits still is when he is in his high chair eating.
Maybe when you are feeding bub's you could give DD a snack if it is around a meal time or if she likes TV put her fav show on TV.
Another good thing I heard is to have a box of her favourite toys she likes to play with and bring them out only when you are feeding the newborn.