1. Do cryptocurrency developers still have control over the cryptocurrency they created after listing Exchanges?
Commonly, yes.
They control the protocol behind the project and can make decisions like burning coins/tokens or changing how it operates.
Bitcoin is different cause it is built on a consensus program, although there exists a core team which weighs in on improvement proposals.
2. After development, how do the developers make their own returns?
• Run an ICO and investors exchange their coins for BTC, ETH, USD etc,
• They could allocate certain amount of coins to the team, which they can sell later,
• They could run an outright scam,
• The could also buy their coins early with the confidence that it would be more valuable if they worked hard at it.