Hi, Cattle and Lambs that go to abattoirs are graded, without getting to much into it you will get grading letters for sheep of say R2, R3L, R3H, it follows a system abbreviated EUROP, to be honest with you I wouldn't worry about it to much. There are always buyers around for small numbers, most areas will have a local agent, who sources cattle and sheep from farms etc for large abattoirs, they will have to supply a regular number so they will be happy to take them off you.
Whereabouts in the country are you? try speaking to your local farmer and ask him/her who they use or look in the yellow pages under livestock dealers. To weigh them you don't need a weigh crate for that amount, a simple way is borrow a set of weigh scales, the type that has a hook at either end for hanging up, they normally weigh up to 100 kilos, find a tote bag that feed comes in they are normally one tonne tote bags, sand also comes in them, there are four handles/loop at each corner, in the bottom cut four holes that you can put the lambs legs through, then with a friends help or if you are strong enough lift the bag up onto the hook of the scales and read the weight, just having three its a easy way to do it if you want to weigh them. There are weigh bands about for cattle and pigs that are like a tape measure, you place the tape normally under the front legs and round the animal like a belt and on the tape it will give you a weight reading, although I have never had any faith in them and never found them to be really accurate.. Hope that helps..