When actors are cast as siblings, one presumes there are screen tests to see how much they resemble one another physically. Which ones do you think are most believable?

William Fichtner and Steven Weber really look like brothers. I also believe Niles and Frasier were well cast as brothers, too.

Hayley Mills and Hayley Mills (The Parent Trap)
Barbara Eden - Jeannie and Jeannie 2 (I Dream of)
Dick Van Dyke and Jerry Van Dyke - Rob and Stacey Petrie (TDVDS)
Paul Petersen and Shelley Fabares - Jeff and Mary Stone (Donna Reed Show)
Jerry Mathers and Tony Dow - Beaver & Wally Cleaver (LITB)
Tommy Kirk and Kevin Corcoran (various Walt Disney films)
Agnes Moorehead and Paul Lynde - Endora and Uncle Arthur (Bewitched)

How about the twins from Everybody Loves Raymond?

the middle… Axl, Sue and Brick