... my dw was 14 weeks along with our first when we visited the midwife, couldn't find a heartbeat, and found out that she was sized at about 8 weeks... two days later, she had a natural miscarriage at home (no D&C, thank you), and was laid up for about 3 weeks.
It's really really hard to be strong after that. Especially once the second pregnancy comes around, and where before there was ecstatic joy, there now is hesitation and doubt. My dw didn't want to believe she was pregnant until she was acting all wonky (vacillating emotionally, and also craving a Whopper from Burger King - but we're both ardent vegetarians!). I asked her to take a pg test - which came out positive! Even so, we waited to tell anyone until we were "in the clear", i.e. further in to this pregnancy than the previous one and we had heard the heartbeat at the midwife's office. Now, we're 23 weeks along and the baby is quite alive and kicking strongly almost every day - a little reminder of our blessing each and every day.
Fatherly advice, hmm... Stay positive. That's hard to do, though, because both dh and dw are dealing with the issue of loss. Because we had a natural miscarriage, I was able to dig a grave and physically bury our first child's remains, and have a funeral of sorts, which helped my dw and I let out our grief together. Not all of the grief, but some. Of all things, don't harbor grief, it needs to run its course. I found grieving alone helped me, and when I felt it well up inside, I simply let it come, experienced it, and then experienced it as it left me.
The more grief I let out, the stronger I became, which was a blessing because my dw was absolutely flat on her back exhausted with all of the changes taking place in her body. I believe that having her stay in bed pretty much nonstop for three weeks while I did all of the cooking and cleaning helped her heal more quickly than anything else; she needed her own space to think and rest and grieve as much as I did. Meeting her needs also helped me in a positive way, offering aid when it was truly needed.
Most importantly, though - stay positive. Miscarriage happens, and I learned that is as much a part of life as birth and each of our eventual deaths. Since our miscarriage, so many older parents with beautiful, healthy, happy children, have told us about their experiences - One miscarriage before their first child, three miscarriages before their first child, four children and then two miscarriages. For whatever reason, the time was not right for that child to come into the world, but that doesn't mean that the time will never be right. Don't take it personally - nothing that either parent did could have prevented the miscarriage. Life goes on, and so must we. To everything there is a season.
Once dw is feeling better, the desire may be to ttc immediately. Doctors don't recommend this, but that's only because they want to be able to date the pg from the date of her LMP. Do what comes naturally - it worked for us.
My personal sympathy to your brother-in-law, I know how hard that is.
love & peace. ~f.