The trick I am learning is to keep them secured and distracted while I am doing something and let them loose when I am not. I get my 4yr old to help me with things I am doing sometimes. That keeps him busy, then I let the toddler watch his favorite DVD. I will switch where the preschooler watches TV and my toddler helps. When I am done, I run around with both of them, play peekaboo, hide/seek, pillow throws, jumping jacks, exercise, pretend games, tickle, paint, draw, write, read, cut paper into shapes, dance to music, let them help with chores, go to the park, ride bike, play with toys, whatever I am feeling up to at the moment, until they get tired and ready for bed. Then I get some peace!
In your case I suppose you could hold your 8mo old and let him/her in on the fun too, pretend you are chasing the other two with her or she/he is trying to catch them. I know it is tiring and takes quite a bit of joggling, but once they are feeling a part of the activities then it gets a bit easier. If you ignore one or the other I think is when tantrums start and it gets overwhelming. Try to keep them all involved.