Maybe you should post a simpler example of what you are trying to do.
For example, here is a simple sequence diagram:
participant "First Class" as A << (C,#ADD1B2) >>
participant "Second Class" as B << (C,#ADD1B2) >>
A -> B: call method1
And here is a simple class diagram:
class "First Class" as A
A <|-- foo1
A <|-- foo2
Mixing both would give something like:
Is this really what you want to do ?
So what we better understand your need, please use some image editor to manually create the diagram you want and post it to https://imgbb.com/
It will really help us!