Holstaurs would be pretty easy. Just get one of those headband things that have cow ears and cow horns on them, then simply make a tail out of some fabric and fake fur. You could also make some fancy pants that have an outer layer of fur on them as well for (part of) the leg bit.
Only real issue is having the right body type i.e. EXTRA THICC, and getting digitigrade legs (if you don't have specifically-shaped prosthetics) if you're a purist and would rather have the whole deal rather than compromising and having human legs/feet.
Elf would be babby's first cosplay difficulty. Just get some ear prosthetics that make your ears pointy, and then act like a huge slut. The rest of her appearance is entirely up to taste, so that can be whatever.