So, if the value read from the serial port is 201, you want to read another value to get the actual angle for servo 1.
If the value read from the serial port is 202, you want to read another value to get the actual angle for servo 2.
Doesn't seem that difficult, to me. Just be sure to not read anything that isn't there, yet. In other words, instead of not reading unless there is one byte or more, as you do now, you need to not read unless there are two or more bytes.
The sender now appears to send a value to define the servo and then a series of values to sweep the servo. That, of course, will need to change, too.