Retrofit solution for door opener and video intercom system

Oh, that's what you mean. Yes, true, you would have LAN with that. But it has the same disadvantages as other powerline solutions, you have to keep that in mind.

I am looking for...

Since the post is already a few days old, the question is what you have decided on? And on the other hand, does fingerprint really work that badly with children? That was my biggest argument for a fingerprint, that the kids wouldn't lose the key...

I'll just answer that: Yes, it actually works quite well only from a certain age. It probably has to do partly with growth and changing fingerprints, and partly it is also a certain motor challenge. Anyone who has tried it as an adult knows what I’m talking about. ;)

We have chosen RFID as an alternative for our little one. You can still lose the chips, but then they can simply be deactivated and the matter is settled. There are even fingerprint readers that have RFID directly integrated, so structurally it is not much additional effort. When she is old enough, it will be switched to fingerprints.

No, unfortunately I haven't yet. Apparently, Somfy was supposed to release the new Doorkeeper by May 2021, after it was already presented at the trade fair in spring 2020. I had hoped to find out a bit more. But aside from general blah blah, they seem to be taking their time or not marketing it without an installation partner. What I liked about Somfy was the relatively simple way to combine multiple access options with the emergency opening. I think I will get some advice soon, since I somehow can't make any real progress.

Last year, nothing came of the retrofit project yet.

I have now started, as the first step, with opening the garage door.
So far, there are only 2 radio receivers for opening the door. This should additionally be expanded with fingerprint options.

As a fingerprint solution, I ordered the ORNO OR-ZS-822.
It looks quite high-quality and is surprisingly heavy and robust.
The device can be operated with chip, PIN, or fingerprint. In the first test setup, it also worked flawlessly with the finger of our 8-year-old child.
I had also ordered the AE Sboard Wiegand controllers. The connection worked with PIN and chip, but the controller was not fingerprint compatible and will be returned. Since I am wiring inside the garage anyway, short-circuiting should not be that easy, so I will omit the additional interface. A break-in would be much easier elsewhere.

For the house, it should preferably be a fingerprint integrated into the doorbell system, e.g., Ekey. But I am still having trouble with the lock.
Nuki works with Ekey, but I find it very loud.
Somfy also works with Ekey, but there is hardly any info about the Doorkeeper in Germany.
For the remaining electronic locks (Danalock, Yale, Tedee), I cannot tell whether they are compatible with Ekey or other fingerprint scanners in any way.

Alternatively, an electronic locking cylinder (DOM, EVVA, Salto, Simons Voss) would also work.
But since these are rather corporate solutions, there is not much information on the net and one would have to get specialized advice.

Maybe there are also new experiences from others.