No, Eager Cleaver is a Long Sword. Hmm... I don't usually LS Tiggy but let's see...
Well if this is his first Tigrex, I'd imagine a very hard struggle. What rank is this? Elder, Low, High? And, sorry, I don't know what Kushala Daora armor does... (too many questions)
Anyway, Tigrex is pretty aggressive and it's weakness is mostly on his front. Although, if you are in front, you can roll under his armpits if you're lucky and/or skilled enough. Like Nobu~ said utilize his turns to hit the head then roll under his armpits.
Also note when he's angry, after to jumps, he rests and does his standing chomping thing. Longest idle of Tiggy, do a slash on the face and roll away. If your brother finds his rage mode a bit too fast, make him use flash bombs.
Don't be greedy, a single slash and then with a back-step slash will be what you'd mostly do.
Other than that, make your brother learn Tiggy's moves. Traps, bombs and flash bombs if you're not confident enough with just a weapon. That's basically it... I think