I'm pleased to hear that Tatty this situation does sound truly altruistic, although I'm anti surrogacy in any shape or form, I understand it was altruistic in that no money changed hands, maybe not even for expenses if the genetic mother and surrogate mother went shopping together for maternity clothes and went to scans together so shared a car, no need for petrol, etc.
As relatives it would be a unique situation, one where the child will know the surrogate mother and the genetic parent. The child will have the chance to ask questions as they grow so they won't have any secrets about where they came from.
I hope the surrogate doesn't have any regrets, perhaps some she couldn't ever admit them to herself, let alone another family member. She may have no connection to the child at all and simply feel joy at seeing her relative as a mother.
I also hope she has her own children already and doesn't long for the child she sees that doesn't belong to her even though she gave birth to to the child. I also wonder if, as 2 other women I know (not surrogates), if she suffered with secondary infertility or miscarriage later if she would feel differently. I can't think of few harder crosses to bear where you might have a child for someone else and struggle to have your own.
(This doesn't apply to the OP I realise, but if the surrogate relative was yet to have her own family and then couldn't it's feasible to think it could cause resentment and issues within the family.)
I'm also pleased the pregnancy went well, so many things can go wrong during and after, anything from a blood loss and incontinence to a prolapse, I would hate to see my relative suffer if she had made a baby for me, only to have difficulties herself. I imagine some relationships never recover in these circumstances.
The woman in this story didn't struggle in this way but she didn't manage to carry a baby to term for the commissioning parents (not being goady, I use this term as noted, I borrowed it up thread) and I can hear the pain in her voice and how she is grieving for the loss of the friendship as well. If doing it for a relative it would be even harder to withhold blame or suggest wrongdoing, and to keep trying and trying, I can't comprehend how that would work.
www.bbc.co.uk/programmes/m0005f2x
It raises the question as a PP mentions, about any health issues for the baby or pregnant mother and how those might be resolved. I'm quite fascinated by multiple births and how they are riskier than carrying a single foetus and how people in surrogacy arrangements manage decisions around this.
Your relatives seem to have had been lucky and maintained a good situation. I hope the surrogate mother's body recovered well and any scars have healed.