Although the legend of the two sisters is a nice story and part of Ormskirk folk lore, it is incorrect. There are two main reasons why the legend cannot be true: first, the legend states that both the tower and the spire were built at the same time, this is definitely not true because the the spire was originally built around 1430 along with the other two spires in it's family around the area, the other spires being at Halsall and Aughton. The Viking settlers came to Britain over a millennium ago so it is impossible for Orme to have built the spire and the tower was built between 1540 and the 1570s, at least 110 years after the spire was built. So not only were they built over 500 years after Orme settled in Britain but they weren't even built at the same time and must have been built by different people all together.
The second reason is that both the tower and the steeple are made out of stone (the spire you see that's on the church now is a Victorian remake after the original fell down in 1731, it was rebuilt in 1790 and repaired in 1826 after being struck by lightning. The original, however, was also made out of stone). The fact that they were built with stone disproves the legend by itself because Viking buildings were predominantly wooden, if Orme did build a church in Britain it would have been certainly made out of wood. It is likely, however, that there would have been a wooden church or building of some sort in place of the Ormskirk Parish Church originally, most likely a place of worship or meeting built by Viking settlers. Viking churches rarely have a tower on the top of them, it was almost always a spire that was built, this means that Orme would have almost definitely built a single wooden spire on top of a wooden church which pretty much disproves the legend alone.
The true story is that the church was built some time around 1170 or earlier, the part of the church which dates back the furthest is the Late Norman Window on the North side of the church, this window dates back to 1170 and is of Norman design so was, obviously, built by the Normans who populated Britain at this time. The spire was built before the tower in 1430 (originally), it was blown down in 1731, rebuilt in 1790 and repaired in 1826 after suffering damage from a lightning strike. The arch piercing the north wall of the base of the spine was rebuilt in 1886. The spire houses one bell, given by the 2nd Earl of Derby in 1521 (before the tower was built), but the bell bears the date it was recast in 1716. The tower was built around 120 after the original spire was built some time between 1540 and 1570.
Sources
The Ormskirk Parish Church guide book.
Wikipedia ()
Mr Traynor and Mr Lyon.