Gary, firstly the fact that you've even considered it at length will mean more to your SIL than you will ever know. My DH and I are soon to be recipients of a known SD (a long-time friend of my husband), but it has been a very long time getting to this point, and going through the process of thinking through who could we ask, what about the relationship down the track, etc. We seriously considered asking my husband's brother (our first reaction was wanting at least some of my husband's family genes in any resulting child) but ultimately decided against it, as the gene issue became less important compared to some of the other issues we had to consider. So, for so many reasons but also for no real particular reason, we just felt better going with our friend. It's been a long and emotional journey for us, and I think the ONLY reason we've made it to this point (with the 3 of us still on the same page) is because of the counselling and their wonderful advice to 'TALK ABOUT EVERYTHING'.

Some of the discussions can become quite confronting, invasive, emotional and uncomfortable (it's some really personal stuff you're forced to talk, think and hypothesise about), and some boundaries can become quite blurry, you will all experience the journey differently and at different times... which is why it's so important to keep talking. The biggest issue we have faced with our SD is that of having more than 1 child. Our SD is really comfortable with the idea of 1, but can't quite get his head around more than that yet. Which was initially hard for me to accept, but after talking with him now I totally understand it- he doesn't know who or where he'll be in 3-5 years or how he'll react once a child exists, so wants to be able to make the call about more children down the track. And as we want our child to know him and have a relationship with him, it stands to reason that any further children are 'wanted' by all of us. I'm not sure what state you're in but in VIC there's also new laws about donors and recipients having to agree on the "disposal" of excess embryos - whether used for science, destroyed, etc

So, as Seachange says, talk to a specific donor counsellor - they'll help you think through all the issues, as it's not possible to even contemplate what some of them might be on your own. And best of luck, it's massive what you're contemplating, it is the ultimate gift of generosity, and your wife and you are amazing people for thinking about it.