Looks like a partially reverted cristate Opuntia.

what you mean by partially reverted?i'm new to this stuff,there's another cactus in the pot with it too,i believe one of themmay have been damaged as a young plant

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dont know if this pic is any better

Yes, the mangled irrgeular looking growth in the centre looks like it was cristate. You can look up examples on google but I'm pretty sure it was supposed to be like that. The cyclindrical growth on the left is the normal habit of the species, although probably a little stretched. The leaves at the tips of the growth identify it as definitely an Opuntia but I have no idea which one. You might want to remove all the normal growth and try to just maintain the cristate bits. You can root some of the normal growth and have a plant like that too.

The other cactus looks like a Parodia. Probably best to put it in its own pot.

some of the cylinders have split 2 and 3 ways at their tops,like branches,should i leave them?and i think there's possibly a 3rd cactus at the backseems to be seperate from the rest and looks kinda different

I'm not sure about the exact species but it is similar to
http://www.desert-tropicals.com/Plants/Cactaceae/Opuntia_subulata.html
but without the fleshy bits on the areoles. I have the same one in my garden although it is not crestate.
If you want to retain the crestate form, then cut off the normal growths or they will take over in time. You can root the cuttings to form new plants.
As to the 'third' cactus, are you refering to the obviously different species (a Notocactus, possibly N. magnificus) on the right side?

Try the link below for a possible ID.

Here is a link that might be useful: pic

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no,see the one,right at the front,paler than the cristate,it's like a pad,with little like balls growing all over it,which have become elongated nearer the bottom of the plant,and there's no leaves in it at all,which makes me think it's different

Looks to be the one plant to me. A mixture of normal, crestate and possible monstros growths.

That does like like a third different cactus. An Opuntia again, perhaps a monstrose one with all those pads all over it.

I see the one you mean now. I can't see the second pic you posted but I can see the growth at the right rear on the first pic. Yes, it looks different. Probably a monstros Opuntia of a different species.

Need help to identify this cactus... Any idea ?

And this one.....

Nesrally-
the first picture is a Euphorbia trigona with a crestate form most likely grafted on the closer branch.

Sorry, but that's not a E. Trigona, it's a E. lactea, I'm pretty sure. Trigona looks quite different if you check it against pix.