Yeth hounds and damage reduction

Also, is the 10hp DR per hit, or total per round? If two fighters hit it for 8 points apiece, will the DR absorb both hits, or will the hound lose 6 hp (16-10 DR)?

I'm worried that if silver is the ONLY weapon that can damage it, it may be too much for my 3rd level party. Also, what about magical damage from spells?

Thanks in advance