Twinkle Body Substitution (煌空蝉, Koutsusemi) is a "Finisher Move" type keyword which debuted in BS43, exclusive to The NinjaTwinkleDragon Siegfried-Jiraiya. Arguably an Advent-based version of Kagemusha, it turns pre-Advent cards into shields to protect Siegfried-Jiraiya from any type of removal.
Q1. Can I summon Braves/Ultimates by this effect?
A1. Yes, you can.
Q2. What if I direct Brave a Brave card or if i summoned an Ultimate by this effect?
A2. Since no Spirit was summoned, the target does not change.