How does this mastery work?

Seducer has solidarity mastery.

Turn 1, Seducer places increase def and block debuffs on all allies.

each ally receives +10 mastery. For how long does this resistance last?

Will the resistance stack with multiple applications of buffs?

Turn 5, seducer places increase defense and block debuffs

Do all allies receive an additional 10 resistance? All allies now have +20 resistance?