Bit of backstory, sorry for length: DS1(30)'s bio father left when he was a baby. It was an unplanned pregnancy and he basically couldn't cope with the commitment. A year later I met my DH, who has been dad ever since. We had two more DCs and have always treated all three entirely equally. Ex drifted in and out (mostly out) for a few years, has never paid a penny in any support, and then we lost contact for quite a while (I discovered he was living abroad, but has since moved back). For the last ten years we've been amicably in touch via social media, have spoken on the phone once and messaged a few times; same with him and DS - they've spoken and messaged but not met face to face since DS was a child. DS doesn't seem particularly bothered - he has his own very busy life, Ex lives a very long way from him, and myself, DH, and the other DCs are his family.
However, Ex did mention briefly at one point that DS was his 'next of kin'. I didn't pursue it with him at the time, but I think this would be correct as he had no further children and has been single for a number of years. He has one other sibling and some nieces/nephews, but that's it. I mentioned this to DS, but we are unsure of what that might mean in a practical sense, and neither of us feels particularly comfortable to ask Ex any more about it.
Also, I do wonder if this means Ex plans to leave his estate to DS, or if this would automatically happen anyway? If this is the case (and here's where I'm probably BU) I can't help feeling that would somehow be unfair on our other DCs after we've strived so hard to keep everything equal between them. In mine and DH's wills we have split everything exactly equally between all three. It doesn't seem fair if DS1 then might inherit a load from another 'dad' who was never in the picture.
DH thinks it's not our business and says if that happens, it is what it is. Also, there's a lot of 'ifs' involved - Ex might meet someone else (he's late 50s) and we know nothing of his business or finances, etc etc. I'm sure he's right, and know life isn't always fair and equal and all our DCs are making their own way in the world now, but still, I wonder if IAB entirely U to feel this way?
Also, can anyone shed light on what 'next of kin' might actually mean for DS?