I worry that the division of the estate one day will damage the relationship between my children of different mothers. What should I do?

Your worry is justified, but the relationship you build from now on is the best protection against estate disputes later. Property often becomes a trial that divides siblings, so instil trustworthiness and fairness in them from childhood. Explain that dividing an estate according to the rules of inheritance (faraid) is Allah's decree to be respected, not a scramble. Avoid secrecy about property; transparency reduces suspicion later. When the time comes, encourage them to settle matters through the Syariah Court or the relevant estate office, and to discuss as siblings, not as rivals. Pray that their love for one another overcomes the pull of property. See children in polygyny.