Helene, your fish maybe tweediei nevertheless. We know that this species is sometimes more blueish; it seems to depend on environmental conditions, especially food. Our friend Prof. Peter Beyer from Freiburg university (Germany) caught at the locations in Western Malaysia himself for several times, and at the same place where the fish had been nearly fully red before, two years later he caught tweediei with much less red and much more blue in the fins.
He made some experiments in Germany with different food, and they resulted in an astonishing change of the colours. But the explanation is not fully complete.
Of course, since your fish are from trade and the trade is completely unreliable in choosing names as they just like, it could be something else, of course. But it can be tweediei nevertheless. If your parent fish look definitely like the unmistakenly red tweediei, then it is very likely that their children are tweediei although they do look more as opallios or alfredi. P. opallios is very improbable because that species is from Kalimantan and has very rarely been traded. P. alfredi is more likely, but the sites of that beautiful species are largely destroyed; I doubt that commercial fishers have much to find there. So, from this point of view it is the most probable solution that they are blue ancestors of the original red P. tweediei.
For decision, you should show the parents to us again.
Another important question is: When did you buy these fishes? P. alfredi has (to my knowledge) not been traded later than 2008 or 2009. perhaps not later than 2006.