Some lines will automatically be easier than others because of the records left behind. The more you know about where to look for records & what makes sense, the easier it is. The more time & money you're willing to spend the easier it is. It's like trying to build a house with just a hammer. It's a lot easier if you also have a saw, drill, screwdriver, etc. With all respect, it's hard to do the way you're approaching it. Making connections between people that you haven't established a connection to yourself can lead you astray. A missing notepad in a Bible would make me very nervous. Because the near relatives have passed you'll have the best luck ordering birth, marriage & death records from the appropriate agency for the parents first, then the grandparents. Fees may apply. Some records may be available for free on genealogical websites as well.
Follow the basic research process for genealogy:
1. Interview your living relatives.
2. Examine your documents and those of relatives that will allow it. Start with your friend's birth certificate. Even if this is the only document they can access it will get you on the right path to find the parents' records.
3. Prepare for research by learning about basic genealogy, genealogy specific to your known ancestors.
4. Organize your data. Free software is available.
5. Research one document at time for one generation at a time for one person at a time.
Repeat steps as needed.
Resources will vary depending on where and when your ancestor lived, what records they left behind, and what is available for that place/time. Not everything is online and/or free. A few hints for making good use of websites: Avoid user-submitted trees/pedigrees except where they have sources cited, and go to the sources. Indexes and transcriptions are better than trees but still likely to have errors. Use these to get you to the original source. Try to find and work with original documents or images as exclusively as possible.
Some helpful starting places:
http://www.cyndislist.com/
https://www.familysearch.org/
http://www.censusfinder.com/
http://www.findagrave.com/
http://www.deathindexes.com/ (U.S.)
Here -- Many of us have resources or knowledge specific to certain documents, times, places, and groups.
Google -- Look for local libraries, archives, agencies, and GenWebs.
Offline -- Libraries, archives, museums, genealogical societies, Family History Centers, etc. BIG note: FHCs have free access to some of the paid subscription sites.