The 1867 marriage certificate for Alexander Shaw ands Letitia Baillie shows they married in Ballynahinch 2ndPresbyterian church. Tradition was to marry in the bride’s church so that’s possibly where Letitia and any siblings were baptised.
Letitia’s father was dead by 1867. Alexander’s father Robert was a Carpenter and by inference still alive. There are several Robert Shaw deaths in the Downpatrick registration area in the period 1867 – 1877 which might be your ancestor. These are not on-line free yet.
You can view the original certificates on-line on the GRONI website, using the “search registrations” option:
You will need to open an account and buy some credits. It costs £2.50 (sterling) to a view a certificate.
Alexander & Letitia in 1901:
Probable marriage for Jane Shaw to Robert Ellison in 1859:
Probable marriage for John Shaw to Martha Jane Kennedy in 1867: