If there are any tup lambs you think might turn out good enough for breeding, you don't have to decide til slaughter point. As long as they are birth notified you can register tups whenever. Any you are sure are rubbish, and you want to castrate them, then make that decision now.
Again, with ewe lambs, you will be birth notifying the lot anyway, even DOAs. As long as you register them by October, you pay the lamb rate. You could still register them next year, but it costs a little more.
Trying to choose which to keep at this age is a bit of a mug's game - there's no way you can see in such a young lamb how they will turn out. There might be a wee cracker or two in there, which strike you straight away as ones you want to keep, but give the others a chance over the summer then decide just before you register them.
Sorry, but it's impossible to judge a sheep or lamb without handling it. A picture alone is not enough info. So let them all grow a bit, get your birth notifications off early if you want, or leave it til later in the year and register at the same time.