Further possession-related things

A thing monoglot conlangers tend not to realize is that possession often is used somewhat differently in different languages.

Consider sentences like

I talked to my mom earlier today. 

I need to wash my hands.

My legs hurt.I have it in my pocket. 

Put it in your wallet. 

My brother is an engineer. 

His brother is an engineer.

Oftentimes, which wallet, whose head, whose pockets, whose mother or brother etc is obvious from the context, and in say Swedish, you'd usually say these along the lines of

I talked to (the) mom earlier today (mamma, morsan; the latter being a diminutive form of moder) 

I need to wash the hands 

The legs hurt 

I have it in the pocket 

Put it in the wallet 

My brother is an engineer (or even the brother, but in that case generally in the diminutive form brorsan) 

The brother is an engineer (generally not using the diminutive, but rather along the lines of brodern; hans bror is also an option, and can be used as well.)

In Finnish, it's not even unusual that definiteness would be ignored in contexts like these, given that Finnish does not usually mark definiteness at all. It does, of course, have possessive suffixes and can thereby mark things like "my brother" as veljeni, but in contexts where whose brother is being spoken of is relatively obvious, it is not unusual to omit this.

There is a lot of possibilities here:

• lexical distinctions along the lines of the use of diminutives or non-diminutives to distinguish owner
• derivative suffixes developing towards being possessive suffixes? (Is that possible?)
• reflexively possessed object marking developing through some odd grammaticalization of the situation described in Swedish?
• extending how often things will be marked for first or second (or even third person) possession - you do not usually say "it's in my street" when something's in the street by which you live, "this time of my day, I usually take my nap", "I am heading out to get my bottle of milk"... this could be very common in another language.