I think I've found the other Comaish child in ManxBMD. The Douglas 1906 scans are so terrible that I gave up and looked at Lezayre (Sulby). These were pretty dark as well, but there appears to be a 1906 entry for Comaish Horace Joseph, Lezayre, B, (think) page 125.
[So Horace, not Harris, if him.]

If you buy this cert as well, do let us know whether they were siblings?

I put the Douglas page number for Dorothy Elizabeth's birth in my message to Liz, above. Vol. A I think, but check with Liz because the online scans are unreadable in places.

You can order certs from the Registry online. See "Contacts" at: www.gov.im/registries/general/civilregistry/

Sue