I have read very few posts on here- other than the first page.
I'll put my input...
I leave my ram and ewe lamb together until August, or September of their first year-- at that point, the ram lambs get removed and turned in with old ewes to breed. I normally do not breed my first time ewe lambs- but some years I will turn rams in Nov 20 and leave in for a month-- will start lambing lamb April 20. This year, I'm thinking about breeding all of my ewe lambs for March lambs- as I'm getting tired of those late/ worthless lambs-- and I'm in expansion mode with my flock.
I also leave my rams with the ewes nearly year round. I do take the rams out for Jan through March, when baby lambs are being born. I've had big bucks kill newly born lambs before.
I try to breed all of my yearling and young ewes to lamb either twice a year, or three times in two years, and so most of the time odd time born lambs are desired-- either in the case of falls for show lambs-- or Mays-- for butcher lambs in the winter.
I turn all of my mature ewes in with rams when I wean-- very often I can get several of them to breed naturally due to hormone swings. The rest of my fall lambings are via CIDRS or sponges.
In the thousands of replacement ewe lambs I have kept- I have had ONE get bred to lamb very early in life. She was a February lamb- that got bred, and lambed in December at 10 months of age-- and raised one of two unassisted. She was also a different breed, and a very early maturing sheep, whereas in the many other breeds we have produced-- most are later maturing.
To the OP- I wouldn't think that leaving your lambs together would be a problem, or breeding your ewe lambs to lamb as yearlings should be either. The only instances where I don't recommend breeding ewe lambs- would be if you wanted to have yearlings big enough to show-- if you are getting babydolls-- you're obviously not worried about having big sheep. The breeding of ewe lambs does take extra care, and time though- but in the long run-- many trials show them to be better brood ewes and more profitable later in life.