Thanks for all the feedback.
I have looked again at the Dublin option and now can get the three tickets for about £2500.
The outbound bit will not be too bad - by the previous poster's comment on flying non stop with kids has got me thinking.
I believe BA are cutting down on people not completing all flights but is there a way I can not do the final lhr-dub leg on the return? i.e. get my luggage at LHR? That would make things a lot easier