There are a numder of online souces.
In particular:
1. The Latter Day Saints (LDS) IGI (at www.familysearch.com), which has many of the Isle of Man baptisms and marriages between 1730 and 1875. Be careful as many are not transcriptions of parish records.

2. Brian Lawsons site (www.lawsons.ca), which provides an index of most of the recorded parish burials and and index of Manx wills. These wills are on film and can be ordered for viewing at a LDS Family History Center

3. Monumental inscriptions. Many have bee transcribed and are available by parish from the Isle of Man History Society.

4. Post 1841, census records

With the approximate birth year of Margaret and Joseph, it may be possible to identify likely parents on the IGI and then with luck find a will or a monumental inscription that confirms the parantage.