Hi @DivaMakosh ,
I don’t want to argue, I just want to straighten thing up. 
In the past, I worked in a broker. Actually, I helped my employer to setup a broker. We started it from white label broker until it became full operational broker. I remembered how I contact the broker, Meta Quote and many other parties for consultation. It was around 2007.
You are correct about $6.6T, (current figure has changed), it was about forex transaction in gov banks, investment bank, retail bank and financial institutions. They are the major player that move forex market. Their transactions make up what we see on chart. As CFD trader, our transaction wont effect the movement.
CFD is derivative product, meaning it will be traded as reference from particular financial instrument. When you trade EURUSD, these two pairs will be the base, for example.
About broker, there are regulated and unregulated brokers. For regulated broker, they will be monitored. They will act as mediator to something so called liquidity (LP). They will earn from commission or marking up the spread. In the past, it was popular DD Broker (Dealing Desk). This type of broker mostly what we called unregulated broker. They will trade against you, our loss is their profit. When we are using unregulated broker, highly likely we will deal with this kind of broker.
For regulated one, they will use LP. Regulator will monitor the transaction, a broker may not go against, so no manipulation to market price.
When you use an unregulated broker, they can manipulate the chart, this will be dangerous. I know exactly how to manipulate price on chart.
Many other scamming scenario , so reputable and due diligent to a broker very important. We can’t assume thing by reading information from internet.
If we are really serious in an industry, we have to learn from head to tail, do investigation directly.