GIS workflow - dynamically creating GML, preserving datamodel and restrictions

An organisation has launched a web service and has specified a data model in GML, with restrictions and constraints, defined and validated by several application schemes (XSD) and GML-1, GML-2. Data often needs to be updated with new data, before upload (as GML) to the webservice.


What I need

I need technical recommendations with prove of concept on a setup that:

lets me append new data to an existing dataset and preserve the restrictions from XSD´s, GML-1, GML-2. etc. and is ready and valid for upload as GML
if possible, open source
can run in background as an automatic task

I have little experience writing GML/XML, and therefore have limited ideas on how to solve this myself - and maybe don't see an easy solution right in front of me. Therefore I will require good communication where you ask for documentation and I will try to find it.

This is the first part of my research. Can you or your company build such a setup - and I can´t build it myself, then I will be willing to hire you for this task, launching a new project on freelancer.


Accessible documentation, data and more
GML application schemes
UML
Guide with examples to write GML(in Danish language, but can partly be translated by me)


My skills - relevant for the project
I have good technical skills - in case you´ll present me a solution that I can work with:

python(advanced)
javascript(little)
node-red (good)
postgresql (good)
qgis(advanced)
docker(good)
ubuntu(good)
leaflet(good)
ogrogr(good)
...and more...

Be free 2 write me for more information. Look also at attached data.