Can namaz be done on Yatim Khana land without trust permission if a nearby mosque exists under Shariah?

In our city one Muslim’s forefathers had donated two connected properties one for mosque and another for orphanages ( Yatim Khana) but unfortunately some group had acquired the property of orphanages and started praying the namaz in acquired land of orphanages instead of coming in the mosque. One who has donated the mosque and Yatim Khana had no objection no restrictions for the other group for coming in the mosque and pray the namaz but due to lack of Islamic beliefs other group doesn’t want to leave the orphanages property. The donor personally had strictly warned not to use orphanages property its Yatims property. The Trust of the Yatim Khana had all the legal documents in their own name but still other group is coming in that area and praying the namaz breaking rules and regulations of Yatims. My question is whether on the acquired land of Yatim Khana having mosque near to it in Yatims place without permission of the trust namaz is possible. What does our Shariah say in the regard of Yatims?