There appear to have been two sons - Guy (1907) and John (1906) Measham Berncastle (plus a third, Frank Measham Berncastle, born after the marriage - deceased 2002).
Herbert's obituary (europepmc.org/articles/PMC2026164/pdf/brmedj03065-0071c.pdf ) says three sons - so they were raised as his.
They do not appear (under Measham or Berncastle, at least) on the consular birth indexes - which unfortunately only means that she might not have registered them. If you know where (what church, if it was a church wedding) the marriage took place you might find a late baptism for one or both boys there. Or perhaps some later record (shipping?) might give you a more exact birthplace.
Not knowing exactly where they were born (or what name they might have been born under) will make getting any info out of Switzerland difficult.