Agree with the others, lambs that young need an absolute minimum of three feeds a day, four is better.
They are greedy little things, lambs, and they will drink more than their first stomach can hold if you let them. If the first stomach overfill, it overflows into the rumen, which is not equipped to digest milk. Bloat will result, which can kill.
How soon they can be outside depends on several factors. They'll need to come in in bad weather and at night, so the outside area needs to be handy for fetching them in. Also, you'll need to be careful about overfilling them, so in general it seems to help to not let them onto grass for an hour after giving them their bottle.
Ewes with lambs are likely to be aggressive towards unmothered lambs, (and need to be in order to prevent them pinching milk), so generally I have found it best to not mix them with family groups until they're weaned.
I used to use a small area of poor, rough grass to introduce my cades to grass. An hour a day at first, in the middle of two feeds, gradually increasing until they're used to eating grass. By four or five weeks, if there's shelter outside for them and it's fox proof, they can stay out full time. (I used to use an old chicken run, so it was fox proof and had a house the lambs could use.).
Then once they're weaned you can try introducing them to a flock with ewes and lambs - but be watchful for them getting bullied by the ewes. It's safer really to keep them separate until there's a batch of weaned lambs they can join.