Crocs unisex-adult Crocband Clog

Why both orange ones(light grey/bright coral or light grey/navy) are out of stock? They look best.

Are these original crocs ?

i bought a size 5, but when i walk without the back strap it keeps falling off. how fit should they actually be? will a 4 be too small?

13 is uk size of us size? please confirm.