Yes. There was plenty of room on that raft
No. Only one of them could have lived and that happened to be Rose
There was enough room for Rose, wasn't there?...
https://www.pinterest.com/pin/426786502158093596/ proved it! See? they were playing CARDS! CARDS on that piece of tingy!
Rose was literally lying across the entire freaking thing. If she had moved her fat butt over, he would've been fine.
Mythbusters proved that jack could not fit