With three kids it's not always easy to give everyone their own space. Especially when our kids all want to hang out in the same area rather than in separate rooms.
Our middle child tried unsuccessfully to teach baby to play with toys in her crib and pack-n-play. And I tried, only somewhat successfully, to teach our older kids to close the door to their rooms when they want to play on the floor without baby bothering them.
Our older kids are learning to be creative and come up with new ways to keep baby away from their toys when they are all together. We currently have a pack-n-play in our living room, not for baby, but for big sister to color, play with Barbies and look at books without baby grabbing her hair or trying to take her toys. Our son even helped her set up stools so she can get into and out of the pack n play easily.
Our dining room table is usually covered with Lego, paints, puzzles, and various craft supplies for our older kids. Baby is still too short to reach items on this table, so it is a great place to put many activities and projects that are not suitable for her. We almost always have a variety of Lego, Mega Blok and Duplo creations displayed on top of bookcases and play dough projects drying on our kitchen counter.
Although it takes some creativity, we are figuring out how to give everyone the space they need. And many times our older kids only want their own space for a moment or two before jumping in and playing with a sibling again.