Unfortunately I don't have any information for the town of Tetela de Ocampo.
Note however that you are able to borrow microfilm of archival documents that will likely have information on your great-grandparents. Specifically, the church archives (1647-1964) for María de la Asunción (Tetela de Ocampo, Puebla) are available on 149 rolls of microfilm. These include baptisms, marriages and marriage banns (the marriage banns can have many details on those getting married and their family), and burials. If you could find these records for your ancestors, it would give you a lot of information about them. Note that once you go back a few generations, it is useful to research the brothers and sisters of your ancestors, as well, as sometimes that is the only way you will find information about your own ancestors.
Also, some of the microfilm has been indexed online, showing names and dates (but the microfilmed images of the original documents will have much more information). These indexes may help you quickly find documents and know which film to order.
The indexes are available on www.familysearch.org
(especially the International Genealogical Index (IGI)).
Also available in microfilm is the 1930 census of Tetela, as well as civil registry archives from 1867-1917 (these include births and deaths and can have details not found in church records; or when church records are not available).
Finally, this microfilm can be ordered at various libraries in Belgium (see the list below).
I hope this helps.
Bergen Op Zoomlaan 20
Antwerpen, Antwerpen, Belgium
Hours: M, T 13:00-17:00; Th 19:00-22:00; Sat 9:00-12:00
Brugge, West Vlaanderen, Belgium
Phone: 32-50 3766 16
Hours: Sat 1:00pm - 6:00pm
108 Ave Henri Jaspar
Bruxelles, Brabant, Belgium
Hours: T, Th, Sat 9.30am-5pm; W 5pm-8.3pm
160 Rue De La Tombe
Mont Sur Marchienne, Hainaut, Belgium
Hours: M 9pm-12pm, 12.30pm-4.30pm; T, W, Th 1pm-5pm; W, Th 5.30pm-9pm; F 2.30pm-6.30pm; Sat 1pm-5pm.
Kortrijkse Steenweg 1060
St Denijs Westrem
Gent, Oost-Vlaanderen, Belgium
Hours: T 9:30-11:30; W 18:00-21:00; Th 19:30-21:00
61 Avenue De La Grande Rotisse
Grivegnee-Liege, Liege, Belgium
Hours: T 9.3pam-3pm; th 9apm-6pm; F 3pm-9pm
Rue Du Grand Tige 45
Erpent, Namur, Belgium
Hours: M 8am-1pm; T 12pm-9pm; F 6.30pm-9pm; Sat 10am-2pm (1st & 3rd), 9.30am-2pm (2nd & 4th)
66 Chauss¿de Braine Le Comte
Nivelles, Brabant, Belgium
Hours: T 5pm-8pm; W 5pm-9pm; Sat 10am-12pm
St Niklaas Belgium
Belsele, Oost-Vlaanderen, Belgium
Hours: by appointment via Mr Jan Krens - 32-3-770-77-37