sending extra luggage in Deutschland

So i understand you want to fly to Frankfurt with all your stuff, send one piece of it to your brother (somewhere in Germany) and continue to the Plata with de rest?
I think this should be possible. There is a post office at the airport. There you should have 2 options, a) buy a cardboard parcel an put you stuff inside (sizes should be listed online) or b) sending a suitcase. The latter is possible since last year, i am not sure if it needs to be a hard case. Option B i more expensive.

edit: this seems to be the biggest size of "PackSet" that they sell. Better be sure that your stuff fits in it. Postage is extra ofc.

@Anhalter, is it still open? I know there used to be one but I don't recall seeing it last time I went through and what I found online it says that it's probably closed. But I still tend to search in English, my German is pretty average...
They do list:
Deutsche Post Filiale 635
P & B Press & Books
Open M-Sat 9.00 - 18.00, closed Sundays
They're listed as a DHL Agent

Up to 10 kg , 120 X 60 X 60 is quoted as €10.49, up to 31,5 kg max €19.99 - same dimensions.

However it is possible that if you have protruding parts for example wheels, handles; & no external packaging of cardboard or paper that they will treat it as a bulky item which costs significantly (€30.00) more. Also the suitcases are not insured for damage to the case itself.

You could of course custom make a box for it, pre-address it and then pack it in the carry-on bag along with some tape and package it once you're in Frankfurt Airport prior to posting.
Suitcase should be closed with zip ties not padlocked. No idea why?

Or, simply use a foldable bag as your carry on and send two packets as shown by Anhalter above


https://g.co/kgs/9x3T2t

@maysie123 , suggest you get your brother to double check this!

@Peterexpatkiwi
Taken from homepage of Deutsche Post itself it seems that the post office is operating daily:

Yes that's the Filiale that I've also referenced above. There used to actually be a full post office not just a Filiale ( they only offer limited services) in the airport but as I said everything I've read has said that it is since closed. No matter it will still hopefully (according to the website) fulfil the required purposes!

There used to be a Post downstairs in terminal 1, by the Meeting Point, but they closed it a few years ago. Sadly.
Am not sure if the new location takes boxes, but from the photos, it is hard to tell.