A proud moment looms for a prominent Victorian racing family with brother and sister Andrew and Katelyn Mallyon to ride in the same Group One race for the first time.

Both siblings will be chasing their first Group One win in Saturday's Australian Guineas at Flemington with Andrew to ride Snitzson for the Lindsay Park stable while Katelyn links with filly Legless Veuve who is trained by Stuart Webb.

"It's definitely the first time we've ridden in a Group One together and I'm not sure whether it's been done," Katelyn Mallyon said.

"It wouldn't have been done too often I wouldn't imagine, and I've drawn next to him in the barriers.

"It's fantastic for Andrew to get the opportunity in the Group One. He's an outstanding rider and he rides winners left, right and centre.

"It's good to get two good opportunities in the race, for both of us."

Andrew Mallyon, who has 48 winners this season mostly on Victorian country tracks, has ridden in three Group One races.

His sister will compete in her 10th Group One race with her best result a third on Heatherly in last year's Oakleigh Plate.

She said there would certainly be some sibling rivalry.

"As you could imagine, there will be lots of 'best wishes' and 'good luck' for both of us," she said.

"The family will get out there and I'm sure they'll get a big thrill out of both of us riding in a Group One together."

The two are the grandchildren of three-time Caulfield Cup winning rider Mick Mallyon.

Snitzson is at $41 while dual Group-winning filly Legless Veuve is at $13 but needs to bounce back from a last-start fifth in The Vanity.

Legless Veuve slipped coming out of the barriers and a post-race scope also revealed she suffered an internal bleed.

"I'm looking forward to being aboard Legless Veuve," Mallyon said.

"We've got a beautiful barrier (six) and I'm not sure of the tactics but I'm sure she'll be positive.

"She pulled up with a minor issue last start and I'm sure if Stuey has got that ironed out,she's going to be a great chance."

Mark Zahra has ridden Legless Veuve in six of her seven starts but is aboard Seaburge on Saturday with Legless Veuve carrying 54.5kg, below his comfort zone.

"She's the type of horse who I think will suit me," Mallyon said.