Using prove an antecedent and your proof rules solve both proofs

Proof #$1.($G$<->$H$)->$I

$|-$ ~I$->($H$->$~G$)$

The first prrof includes $16-20$ lines

Proof #$2.$ R$<->($S$<->$T$)$

$|-($R$<->$S$)<->$T

The second proof includes $44-50$ lines