it's horrible when they won't sleep hun, and incredibly frustrating.
a few things i used to do with ds2 (who was a really bad sleeper) was:
carry him around in a hug-a-bub and let him sleep on me- this allowed him to get used to sleeping for longer periods and not be so over-tired.
put both boys in the pram and walk around until ds2 was asleep and then park the pram under a tree and take ds1 to the playground to spend some one on one time with him