Does my first marriage son have rights in HUF property?

I applied for HUF PAN after my 2nd marriage, with date of incorporation as the 2nd marriage date. HUF deed mentions wife & child from 2nd marriage only (I did not include son from 1st marriage since he always stayed with ex-wife & she got full custody). My father gifted his self-acquired house to my HUF. My 1st marriage son (major now) is demanding a share in that proportion, saying its ancestral. He found out that the house was given 2 HUF. Despite that, insisting share & threatening court case. I asked lawyers: 2 lawyers said the 1st marriage son doesn’t have rights in HUF assets since we never stayed together. Another lawyer said: all my descendants are automatically part of HUF. So looking for clarity: 1. Was it ok to mention 2nd marriage date in HUF PAN & excluding 1st marriage son in HUF deed? If not, will HUF become invalid? 2. Does the 1st marriage son have rights in HUF prop, though his name is not there in HUF deed? 3. If son takes matters to court, does he have a strong case to win? Can court grant interim stay against selling HUF prop?