Ruperts sibling

[Christine88]

Baby number 2 due in 8 weeks, another boy! No name ideas yet!

[ThroughThickAndThin01]

Henry
Oscar
Edward
Tobias
Hugo

[WellErrr]

Caspar!

[Iliveinalighthousewiththeghost]

Alistair
Arthur
Edmund
Charles
Lucian
Timothy

[AuntieStella]

Marcus, Alexander, Piers, Giles, William?

[Nanasueathome]

Arlo
Samuel
Jonah

[Angelto5]

First thought was Dexter.

Please be aware if you do call your ds Giles,some people will assume your a Buffy fan as there is a character called Rupert Giles.

[rosieliveson1]

Rupert and Henry or Rupert and Theodore

[wannabestressfree]

Monty

[imsorryiasked]

Felix
Edgar
James
Jackson

[GooseberryRoolz]

Algernon

[OneMagnumisneverenough]

Miles
Crispin
Elliot
Barnaby

[OneMagnumisneverenough]

Guy
Lucas
Edwin
Frederick
Benedict

[OneMagnumisneverenough]

Sebastian
Sylvester
Merrick
Dante

[OneMagnumisneverenough]

Actually I think I have to scrap Barnaby - you need to be careful of ending up with a bear theme!

[LadyAntonella]

Arlo

[Leigh1980]

Tarquin
Caspian
Rufus
Jonty
Miles
Hector

[BigGreenOlives]

Tim & Simon (true live brothers to a Rupert. In their 50s now. The other Rupert I know doesn't have any siblings (also 50s).

[WhyCantIuseTheNameIWant]

The one I know had a brother called Oscar.

Jasper
James
Hugo
William
Frazer

[mutteroo]

Love Caspar as already suggested

Also like:
Theo
Arthur
William
Alfred
Nico
Luka
Milo
Asa
Louis

[ShmooBooMoo]

Jasper

Edward

Miles

Bertrand (Bertie)

Alistair

Freddie

William

Hugh

[SealSong]

Max

[5BlueHydrangea]

Toby / Tobias
Gregor / Gregory
Alexander
Elliott
Edmund
Max..
Michael
Christopher

[HeteronormativeHaybales]

Some good ideas here. Oscar fits especially well, and Edward, Max, Henry and James would be good choices.

I think you should go for 1 or 2 syllables.

Reuben (if the similarity of the opening sound didn't bother you)?
George?
Adam?

[mcswaz]

Would you go double R? Rupert and Ralph?

[BlueChampagne]

Conrad
Ambrose
Anthony