I guess Brazen Def/Res is an option, though I prefer Brazen on Vantage/Desperation units.
I feel Brazen skills only benefit Vantage and Desperation when they work with them, which DEF/RES doesn't really. Brazen ATK/SPD or ATK/DEF works great with Vantage while ATK/SPD works best with Desperation. I should know due to my awesome Lyn with Sol Katti Forged, Brazen ATK/SPD and Vantage.
Brazen DEF/RES I feel works on Mixed Tanks, like for example:
-Hardin, Grima, Gwendolyn, Sheena, V!Eliwood, H!Jakob and Winter Lissa for Armors.
-Selena, M!Kana, Summer Robin, Joshua, Fjorm, Hawkeye, Lissa, and Faye for Infantry.
-Camilla, Narcian and Myrrh for Fliers.
-Berkut and Spring Xander.
Than there's the Units with a forged Berkut's Lance. Let's look at Oboro with a forged Berkut's Lance. She will have 35 DEF and 35 RES at neutral each when attacked. Combined with Brazen DEF/RES, she'll have 42 DEF/RES each. Than add in Close/Distant Defense. That'll reach 48 DEF/RES depending on the foe. Than have a unit with DEF & RES Tactics. Oboro will reach 54 DEF/RES against a Close/Distant opponent.
Either way, Brazen DEF/RES will be something very fun to try out.
Is there a way to fight your friends in FEH?
Nope. There's no PVP. However, in some events, you can have your friend's units join you and you can use them.