How to unite three different batteries in to one powerbank
It is possible, but not advisable.

First a little background information:


Putting batteries in series adds the voltages together.  This does not add the capacities together.
You put batteries in parallel to add the capacity.  This applies to current as well as capacity.
You normally put batteries of the same size together to make a larger one.


Lithium batteries are not something you want to play with.  If you mistreat them, they can (and will) catch fire.  And, it is almost a given that you will make a mistake in what sounds like your first project.

It is possible, but you will have to do a lot of things that will make it simpler (and cheaper) to buy a proper power bank.


You will need a separate charge controller for each of your batteries.
You will need a management circuit for each battery.  This monitors the discharge state and disconnects it from the load when it is too low.  It also has to protect against charging a low capacity battery from a higher capacity battery.
You will also need to control the discharge rate of each battery separately.  Each battery type has a maximum discharge rate (maximum current it should be allowed to deliver.)  Three batteries, three discharge rates.


For each of those components, you will have to provide proper settings matching your three batteries.

That's a lot of information to collect, and for at least one battery you don't even have the basics, let alone the specifics.

If you ever get all that together, you need a boost converter to convert the voltage from the (nominal) 3.7V to the 5V normally needed as the input to your cellphone or other device.

All of that can be dealt with, but it is a lot of stuff to deal with.
I'm a hobbyist who has built a lot of stuff, and I wouldn't do it - too dangerous for too little gain.  

The engineers here wouldn't do it, either.  So much to do to make work and make it safe that it isn't worth the bother.  They'd specify new, identical cells and use battery controllers appropriate to just that one type.

Long story short:

Don't do this.  It isn't as easy as it looks, and you could burn your house down.