Example: Using a ERC-1155 contract for real estate, Say I have a 100 acres of real estate i want to lock into a ERC-1155 vault to then fractionalize with 100 ERC20 tokens. I want those ERC20 tokens to be indivisible so users can't own a half of a token, only 1 token. Is this possible?
The thing is that ERC20 tokens are fungible and normally they are divisible. This is the idea of fungible tokens. But you can always have your own implementation of the ERC20 token which will behave the way you want.
On the other hand, you are talking about something that is non-fungible. And in the case of 100 acres of real estate you want to fractionalize, it's better to use the ERC721 token, which is non-fungible. With the ERC721 token, you will not have the problem that the user can own just a portion of a token.
I think this article could be helpful for https://101blockchains.com/erc-1155-vs-erc-721/