Pride of Le Havre and Pride of Portsmouth were originally built for Olau Line for their Sheerness to Vlissengen service and were delivered in 1989 and 1990 as the Olau Hollandia and Olau Britannia. Olau Line was shut down by their parent company in 1994 and P & O chartered the Hollandia and Britannia. They were renamed the Pride of Le Havre and Pride of Portsmouth and both were used up to 2005 when the Portsmouth - Le Havre route was shut down by P & O.
Estonia was delivered in 1980 as the Viking Sally and was used on ferry crossings between Finland and Sweden initially. It was acquired by Estline in 1993 and renamed Estonia.
Pride of Le Havre and Pride of Portsmouth certainly were sister ships, but it appears there is no connection at all with the Estonia, given they were built 10 years later than the Estonia.