I routinely expose my ewe lambs to the rams, as long as they have grown enough, size and weight is more crucial than age here. Usually 50% will conceive, some years more.
If yours were April lambs I would think it worth a go.
My neighbour has 1000 ewes and is growing his flock, he puts his ewe lambs with the rams and the ones that lamb, again about 50%, he retains in the flock. The ones that don't, we pull out at shearing time and they are kept seperately through the summer and sold in the fall as yearlings for big money, they look really good by then. His are Cluns, mine are Dorsets.
As to Dystocia, don't get them too fat, but feed them well?! and if possible give them some exercise in the 3rd trimester. Cooped up in a little space stuffing themselves because they are bored is not good.
Then, when they are due to lamb, be aware of them, be prepared to assist, but 9 times out of 10 you will find it all goes well. The object is a nice healthy single, for her to learn how to be a Mum on, this is what usually happens. Twins can require a bit more attention getting started.