Im a trombone player, and my main type of music is ska. 57 does work good if thats all you got. But i really like to use the AT4033 on the horns. Its about $350 with shipping at most places and its a great all around mic. For position, i recommend being about 3 meters away from the mic. You shouldnt have a problem that far back with pointing it directly at the mic. However, if your trombone player is a load player you might want to bring the mic a half a foot from the bell. Some people say to then point it up towards the bell but i found that that gives a really weird sound on horns. Keep the diaphragm straight forward just off axis of the SPLs and you should do alright.
This same position might work for with the 57 also. I recommend having it back a way from the mic to let the bass frequencies form. You might have to use some compression also to make it stand out some. Also, the AT4033 (Audio Technica) is very good with vocals too and just about everything. The 57 is great for recorded guitar cabs so if you can afford both i would recommend it.
as far as trumpets go, you could probably get a little closer to the mic (if the player is not extremely loud). The trumpet does not have as many low frequencies as the trombone.
Oh, one more thing i should mention. Your room will be a huge aspect on how far you can be from the mic. I recommend throwing up some blankets, sleeping bags, bed foam, etc to try and deadin the sound a little bit if are having problems.
Good luck.
Darnold