#this is just my stephcass goggles but. i do think stephanie should be a point of contention for them

[casscainmainly]

is cass closer to tim or duke as a sibling??

As much as I love Duke, it's 1000% Tim.

Cass and Duke is a relatively recent relationship, mostly contained in Batman & The Outsiders (2019). I think in certain instances Cass might like Duke more than Tim because they don't have as much history, but in terms of closeness, Cass and Duke have never had the depth of relationship Cass and Tim have.

We have their interactions in Batgirl (2000) #18:

This issue opens with Cass dreaming that the Batfam turn on her after finding out she's a killer. Tim in this issue serves as proof that they can accept her, which makes Tim pretty important to Cass' feelings of belonging in the family. Cass associating Tim with being in the family is something that continues for most of their relationship.

Then we have the iconic team-up in Robin/Batgirl: Fresh Blood:

There's a lot of tension between Cass + Tim in the wake of Stephanie's death, particularly in their attitudes to Bruce. But there's also a sense of shared grief - here, Cass opens up to Tim about David Cain shooting her, something she talked about with Steph before. She's not exactly secretive about her past, but I don't think she opens up like this to any of her other brothers, even Duke. I think it's important that Cass knows Tim loved Stephanie as much as she did (and possibly more). It's a source of tension, but also a source of connection.

Although he's a little out of place, it's why Tim is there during the adoption scene in Batgirl (2008) #6:

Following from #18, Tim kind of symbolises Cass' acceptance into the Batfam (which makes sense, since other people have talked about Tim essentially creating the idea of 'Batfam' in the first place). In Fresh Blood, Cass' break from Gotham + the Batfam is shown through her and Tim deciding to go separate ways, which is why her induction into the Batfam has Tim there and smiling. Tim also repeatedly defends her in this run, which could mean something if any writer ever referenced this series beyond the adoption.

Their most poignant moment for me though is Red Robin #17:

It's obviously editorial shenanigans that stopped other writers (particularly Bryan Q. Miller on Steph's Batgirl run) from using Cass, but as it stands Tim is the only one who kept in touch with Cass during her stint in HK. We have this really lovely scene where Tim hands her a Bat symbol and says they're still family, no matter what she's called. Black Bat is arguably a big homage to Red Robin, and certainly at this time she was closest to Tim out of literally everyone.

They have more moments Rebirth onwards, but basically Tim is a really really important part of Cass' journey into the Batfam, and sometimes was her strongest (and only) link. Though Cass' relationship to Duke is maybe the smoothest of her brotherly relationships, Tim is undeniably the brother she's closest to, the one who knows her best and who's seen her through the toughest times. So although Cass might say Duke is her favourite brother, her real favourite is probably always going to be Tim.