Generating the same private key, or generating a different private key that generates the same public key is very unlikely. Sending money to is will give it the amount you sent, there is no dividing. Its a normal public address like any else, but it may be controlled by multiple users if they both have the key.
Apparently, there can also be two private keys connected to the same address.
Link: Two Private Keys, Same Address
"Yes, you can have two keys generate the same address .
There are 2^160 possible addresses, and 2^256 possible private keys, so each address corresponds to roughly 2^(256-160)=2^96 private keys. Any of these will generate the same address and thus be able to spend the money owned by that address"
Here is a funny website to check out: https://keys.lol/