I'd take the second lamb and put it in a dog crate under a heat lamp for 2 or 3 days, feed it colostrum and then bottle feed it. I assume that this is your only sheep? I'd put the lamb back in with the ewe after 3 days (in quite a large space), the ewe will attack the lamb and the lamb needs to have enough space to be able to get away from her. I'd keep them like that, the bottle fed lamb will come to you for food and hopefully stay near the ewe for protection. After a week or so I'd let them into a small paddock, back in at night for a month or so as the ewe won't protect the bottle fed lamb from preditors