Hi Elwyn.
Can I ask if Alexander is also buried at Tamlagh Parish Church.
Furthermore I understand Robert also had a daughter called Winifred, do you know when she was as born?
I don’t know if Alexander is buried in Tamlaght graveyard. There’s a transcript of the legible graves in Tamlaght Lower on this site. There’s no McComb listed but he might have been buried in an unmarked grave, or the stone may not be legible now.
http://www.oneirishrover.com/tamlaght-graveyard/There are quite a few other graveyards in the area. Not all have been transcribed and not all are on-line. You may just need to go round them all and search.
Winifred’s birth was presumably in the 1930s or later. Births in Northern Ireland within the past 100 years are not generally available on-line. They are open to the public but just not on-line. There are 2 places with on-line access: PRONI & GRONI (both in Belfast). If you, or a researcher, can get there in person you can search for her birth there. Otherwise you would need to contact GRONI (by e-mail or by phone) and ask them to search for you. There may be a search fee in addition to the cost of the birth certificate. Contact details for ringing or e-mailing GRONI:
https://www.nidirect.gov.uk/contacts/contacts-az/general-register-office-northern-irelandI think Gaffy & Aghadowey have already answered your other points.