1. I could eat some of them. (OK)Originally Posted by idwt
2. I could eat some of them cakes (Not OK)
3. I could eat some of those. (OK)
4. I could eat some of those cakes. (OK)
Sentence 2. is Not OK because 'them' stands alone. It cannot modify a noun (i.e. *them cakes is incorrect). Sentence 3. and 4. are OK because 'those' can modify a noun (i.e. those cakes is correct) or 'those' can stand alone.
By the way, yhere are dialects of North American English in which "them cakes" is used, but it's not representative of the Standard North American dialect.
All the best,