I think Alistair goes better with the other two names, even though it's a syllable longer. I mainly don't think Hugo & Jasper sound like brothers.
In fact, I think the better sibset would be Silas, Alistair & Jasper.
Please rate my personal short name lists (the latter includes combos):
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/91835 (updated)
http://greens-end.myminicity.com/env