Suing a developer for delay in property handover following the death of father

My late father had purchased a 3 BHK apartment in a project in Ajman from a developer for around 500K. They were meant to hand over the units back in 2009-2011.

They had then offered to buy another project, and as usual, had promised that even that project would be delivered within months in 2012, which we respectfully declined as then property agent was hopeful that the B15 tower's court case would be resolved soon.

My father tried countless attempts to follow through with the team of the developer and recover his funds as we had paid up to 90% or just the last cheque of 70,000 was pending for full payment towards the property handover.

However, fast forward 2020, my father passed away in January 2019 and never saw the light of the day for that property and now my sister and I as his heirs are going round and round with the real estate agent again.

I would like some serious advice on how we can recover the funds from the developer.