You're not supposed to store seeds online.
Also, you're needlessly complicating issues.
You can write everything down on a paper and store it in an offline location like a safety deposit box.
If you want to split your seed, then you wouldn't store it in plaintext, but instead using something like Shamir's Secret Sharing.
The website below gives a demo
http://point-at-infinity.org/ssss/demo.html