Oh my gosh...
At least you are in communication with the Husband.
For as much as he can communicate or tell you things... being in this situation.
One thing to watch out for is: if Depression due to grief, is occurring. I don't know if you can, but give the Husband a head's up, he will need to look out for himself and his Wife, per her well being.
Grief, is a multistage process.
When my Dad died, my Mom, found a "Grief Support Group" which was for ANYONE going through a loss of any kind. It helped her immensely because everyone there was going through the same thing, and thus, they could commiserate and grieve, without feeling they had to put on a "brave face." It offered my Mom, needed support, which was beyond what me or my family could do for her. So that is one tip.
Also, they may not want visitors at all.
It is a very lonely and sad time. A person does not even know how... to "grieve." They have to find their way. But yes, offer them whatever support they want/need/can manage to ask for. Many in this position don't even know... what help to ask for. Or they may not ask for help because it is a very lonely and sad thing. But yet, they may want to be alone. Just as a couple and need "privacy."
Helping with their kids, will probably be nice. But they have their Grandparents too. And the kids may want to be with their family, too.
My friend, lost a baby in the last trimester too. She had to, go through the "birth" process despite her baby being not alive. But she didn't tell anyone, until much later and until then she and her Husband just did not socialize for a bit. It was hard.
My own Mom, lost a baby at birth. It was stillborn. The Doc, did not know. In those days well, medical knowledge was not like it is today. She went through a lot of emotional trauma during that time, blaming herself etc. But it was not her fault, of course. And she also had to put up with relatives/people, being "nosy" about it and telling her what she should have done different etc. while pregnant. Which of course, they thought they were being "helpful" but is in actuality very rude and cruel to a woman who lost her baby. Every Mom does the best they can and know how, while pregnant. But a woman may go through stages of blaming, herself.
I had a miscarriage once. But that cannot compare to what your friend has lost. But even for me, I did not want to talk to anyone about it. I had to, meander through it by myself, with my Husband, only. I did not want anyone telling me anything or doing anything "for" me. That was my, way. Even my Husband, had a very difficult time... talking about it and dealing with it. But it took months, to adjust to and to feel "normal" again.
I would think, that after your friend's surgery... they would want to be by themselves. Calling people about it... would probably be a very hard thing for them to do... and they will call or the Husband will call... when he is up to it.
Grief is a very hard thing. Especially for a baby that was lost at this stage.
Tread carefully... go by their... cues.
Listen to their cues... carefully. Because in this situation, people are not real articulate nor succinct in their communication. They may not want to be "rude" and say "no" to people who offer them help, but so they may just accept and go along with it, even if they are uncomfortable with it. I was like that. For example.
See what the Husband says. Then proceed.
The best thing you can do is to let them be.
But say you are there for them. But don't push.
And be observant to if any depression is occurring.
One thing I might add: When I had a miscarriage... the LAST thing I wanted to do was to be around people, even my closest friends. Why? Because, being around people meant, that I had to talk about it, or remember it... over and over and over and over and over and over again... repeatedly, each time I was around a friend or on the phone with someone, or in the company of others. And that was not something I needed nor wanted to do. For me, I had to just be by myself. Only with my Husband. The last thing I wanted was to be on the phone. I needed quietude etc.