I have been reading "The Greeks in Bactria and India" by W.W. Tarn.
He offers a very plausible reconstruction of events with Demetrius considering himself having a claim to the Mauran Empire due to marriage connection and relying on Apollodotus and Menander as his subordiantes to mount a pincer movement on what had been the Mauran Empire. His thesis collapses, however, if the alternative dating of Meander that places Meander significantly later is accepted.
In 'Civil Wars and Alliances in Bactria and North-Western India after the Usurpation of King Eucratides' François Widemann considers Tarn's thesis as so discredited to be barely worth arguing against. I am reluctant to take Widemann's word for it as this rejection seems mainly negative. That is to say that the alternative to Tarn seems to be an incoherent list of possible dates of reigns with not even a hint of the motivations behind that.