Can an activity diagram and seq diagram be implemented in parallel?

Question

There are steps which are to be done parallel in activity, seq diagram

Answer 1

I believe what you are looking for is a parallel processing fork in an activity diagram.

@startuml
start
fork
:action 1;
fork again
:action 2;
fork again
:action 3;
fork again
:action 4;
end merge
stop
@enduml