For RAR Bair, you have to flick the stick. I always think about a RAR in two parts, (it makes it easier for me anyways).
1)Before pressing jump - to RAR you need to be in wolfs run, not dash animation. Wolfs dash is super short, it only takes about a battlefield platform to go from dash->run. Once in the run animation, flick the stick the opposite way your running, this causes wolf to turnaround. Wolf will even be turned around (once he's airborne) if you flick the stick and jump 1 frame after.
2)During jumpsquat - jumpsquat is the 4 frames where wolf crouches before jumping when you press the jump button. Your directional input at the end of jumpsquat determines how much momentum wolf will conserve going into his jump.
So if you want to do a full momentum RAR back air, your gonna dash (let's say right arbitrarily) briefly until wolf enters the run animation (only ~1/2s), jam the stick left (before jump), hit jump (your now in jumpsquat) and jam the stick back to the right (stick has to be back over to the right before jumpsquat ends). You know you did a full momentum RAR if wolf does a backflip and lands facing the opposite direction he initially ran.
tl;dr - if your running right, flick the stick left, press jump, flick the stick right before jumpsquat ends, boom! full momentum RAR.
Regarding marth, marth is the king of punishing missed sweetspots. Marth can't fsmash you if you sweetspot. I find up B a little tricky to sweetspot with it's weird momentum conservation for the charge up and the huge range you travel, but practice makes perfect, so hit the lab with the ledge grab box enabled and you'll eventually get a feel for the sweetspot range. Side B is a lot easier to sweetspot, and hella fast. I think you should almost always opt for a side B if it will reach (below stage anyways, above stage you can angle up B into the edge for a tricky recovery, or fly in multiple directions on stage) it's faster and easier to sweetspot and has a juicy hitbox that might jank them if they try to grab ledge. Shine stalling is a great way to mix up your recovery too, toss some in to mess with your buddies timing.
Remember side B can be angled up or down to help snap to the ledge. You can shorten it too, but shortens off stage are risky as it only takes 1 frame of error to potentially SD.