1:01 PM PT -- Donald Trump has responded to the picture of some members of the Walz family ... thanking Tim Walz's brother, Jeff, for the support. The problem is ... Jeff is not in the picture, Mama Walz confirms to TMZ.

Democrats might be surprised to learn some members of Tim Walz's family are riding the Trump Train -- but the VP candidate's mother says it's not a big deal because they're the conservative wing of the clan.

Walz's Nebraska-based family members are firmly behind Republican Presidential nominee Donald Trump, which is highlighted by a photo posted to X showing them wearing MAGA shirts.

Charles W. Herbster -- a conservative who has run two unsuccessful campaigns for governor in Nebraska -- posted the pic to the social media platform that features eight people wearing "Nebraska Walz's for Trump" shirts.

Darlene Rose, mother of the VP candidate, told TMZ ... although the picture is legit, she's not shocked by what she saw in the image from that side of the family.

According to Mama Walz ... the fam in the pro-Trump picture are second cousins to Tim ... and they are conservative, devout Catholics ... so, again, not shocking.

That said ... Darlene tells us she was not too irritated by what she viewed as a stunt … she still has full confidence in the Harris/Walz ticket.

Still, the photo's blowing up on right-wing social media pages right now ... with some people pointing to it as proof TW doesn't deserve to be the VP -- 'cause he can't even get his own fam to back him.

Like we said, there's some distance between these family members and Walz ... but, they aren't the only family members publicly blasting Walz -- with Tim's bro Jeff telling his Facebook friends last week not to vote for Walz.

ICYMI ... Jeff clarified his political position -- saying it doesn't align with Tim's own, and adding "The stories I could tell. Not the type of character you want making decisions about your future."

Jeff made it clear he and Tim haven't spoken in nearly a decade ... and, it doesn't sound like the frostiness is ending anytime soon.

Tim may check the box next to his own name on Election Day ... but, sounds like at least a few Walz family members are going in the other direction.