Is it possible to have my blockchain on a different folder than that of my wallet files?
For safety and integrity reasons, the wallet file must be held within the datadir. You can choose a different file with -wallet=&lt;file&gt; (config or startup argument). But only a filename not a path.
Don't try to share your wallet between multiple bitcoin-core instances. 

What you really want to do is multisig.

You could have a bip32 watch-only wallet with a 2of2 multisig (you can watch the funds, but not spend/sign).
With additional hardware wallets (like an USB stick), something like Trezor or digitalbitbox.com you could – in theory – sing the desired transaction and therefore complete it and make it ready for broadcasting.

But, unfortunately, it's not possible with current version of bitcoin-core without entering the RPC world and also patching and self-compiling bitcoin-core.