Something I've noticed is This whole family has insecurities about themselves and they make them feel like they dont fit in but they all help each other deal with those insecurities in the most supportive healthy ways
Making each character feel like they do fit in somewhere

Splinter
Splinter fears that he is nothing but a rat but he tries to hide those emotions from his children because he doesnt want them to feel sorry for him
But his kids constantly show him that he means so much more to them and isnt just seen as a rat to them but their dad

Raph
Raph has insecurities of his stinks and size when his brother mention his fear stink in the first episode we see how defensive he gets about it
But his brothers never make fun of raph for his stinks
We also know raph is claustrophobic possibly due to that reminder he is

Huge but his brothers all love how big he is and make him more comfortable in that size by constantly hugging him and telling him how beautiful he is in his own way

Leo
Leo is insecure about his skills and what he brings to the family
He knows raph brings the muscle donnie brings the tech and mikey brings the optimistic energy but leo feels like he doesn't being anything to the team
He tries to hide this under jokes abd smug smiles but

Deep down that all comes from a pain he has
hes aware his family doesnt really have much faith in him and see him as a clumsy doesnt really take anything seriously guy

Leo tries so hard to prove hes more than that constantly because he thinks that's the only way his family

Will accept him but they all already do sure leo gets in they're nerves but they all really do love him and trust him too they know hes git a smart mouth and they trust that to help them out of problems
They know hes also smart enough to know exactly what to do too helping leo

Feel a little more accepted in the family for who he is
But he still wants to prove hes more than that too which is why he loves to win everything he can