Is a new sum of money collected from the government specifically for building a house to be combined with the joint money the father manages for the purpose of paying Zakat, knowing that the new money has entered a private account and the file has been under study for a long time?

Both the father and the son must pay Zakat (definition) on their wealth separately if it reaches the nisab (definition) and a year has passed over it. The mixing of cash funds has no effect [on Zakat] according to the majority of scholars. The amount utilized for building a house begins a new hawl (Zakat year) from the date of its acquisition, and Zakat is paid on it after its hawl if it reaches the nisab. If it is spent on construction before the completion of its hawl, then no Zakat is due on it.