Have been living for a year in a pure stone house... Concrete foundation, concrete walls... a real bunker...

but a very nice and robust house....
Anyway, we've now got a wild idea to renovate the bathroom on the ground floor. In connection with this, we face a couple of interesting problems...
We want to make an opening in one of the partition walls (thickness about 10cm, concrete) and we will also need to install an additional floor drain in the bathroom...
Not a job for happy amateurs, you quickly realize... but does anyone have experience getting work like this done? We need to make an opening in a partition wall that should be about 1200 x 2250
Regarding the floor drain, there is already one in the space, is it possible to somehow create a hole for an additional floor drain and then connect to the existing one, or how do you do it?
Can anyone recommend a craftsman or company in the Skåne / Malmö area that can perform work like this?
Very grateful for tips and advice, I've searched and searched but don't think I find much info about making modifications to concrete constructions....
Stefan