Firstly - good luck with the process!
I have a BMI of 42
I know, I know. We were unanimously approved at panel last June and are hoping to be matched soon, as we've had a bit of a rocky road since adoption panel approval.
I can honestly say my weight was never an issue BUT this was probably because I have a good resting heart rate, low blood pressure and no health issues at all. Like you I carry my weight really well and people are shocked if I tell them how much I weigh. I made it clear that I'm aware being overweight is unhealthy and I did lose just over a stone sensibly before panel (have comfort eaten it back on since but back on track now).
We are going through our local authority rather than an agency so this may be worth exploring too (I can't speak highly enough of our SW but I know we've been very lucky).
We were asked why we wanted to adopt which is one of those deceptively simple questions you can tie yourself up in knots with. We went with the simple and honest "we'd love a family and we think we have a lot to offer". Realising that the children are at the centre of the process (families for children, not vice versa) is also a good start, as your family member will probably confirm.
Yes to talking about your current support network if asked, I would also acknowledge that this will likely change and develop as you go through the process (our certainly has and we have made some good friends along the way).
Think about your current childcare experience and be open to expanding this via volunteering (e.g. kids clubs/nursery/school/relatives). You can relate this to the kind of ages of children you are hoping to adopt - again, try to be flexible and open about this. Realising that parenting adopted children will be totally different to birth children is important too. The fact you have an adopted child in your wider family will be really helpful in demonstrating an understanding of this, though of course every experience is different
Our initial meeting was about 3-4 hours as we got chatting and it covered both our family histories, significant events such as bereavements and so on. I've had some tragic losses and these were explored, but in a supportive way. It's very much about demonstrating how you have learned from life experiences, building resilience etc.
Things that I was worried about being seen as a negative were viewed positively, e.g. having experienced loss I would be able to empathise with an adopted child.
They may also ask about your relationship - how you met, how long living together etc
And probably lots more but I can't remember!