The multiferroic perovskite BiFeO3 is the only material that displays both ferroelectric and antiferromagnetic order at RT. Significant efforts are aimed at better understanding the structural phase transitions that occur as the Bi and/or Fe are substituted with isovalent ions, e.g. lanthanides at the Bi site and Mn or Cr at the Fe site. Prior to the structural phase transition an increase in the ferromagnetism is often observed, and it is has been speculated that this behaviour is intimately linked to the collapse of the long wavelength spiral spin structure that is a signature of BiFeO3. Despite the strong connection to magnetoelectric effects, the magnetic structures in particular remain poorly investigated. Here we plan to study the evolving crystal and magnetic structures of 3 series of substituted BiFeO3 and link the diffraction data to magnetisation data on the same samples.