Pipe behavior is erratic, not confident about implementation

I am learning about ipc in Linux and trying out pipes. I've set up two pipes between the parent and two child processes. While the data goes through the pipes, I get weird newlines. For instance, the output would sometimes have an extra newline or no newline entirely or even appear on the command line itself. Also, I am unsure whether the way I have set up pipes is correct. I may have overlooked some important details and leave dangling file descriptors.

void run_processes(Command_Args *cmd_args, char *file_paths)
{
        pipe(pipe_RtoA1);
        pipe(pipe_RtoA2);
        pipe(pipe_A1toT1);
        pipe(pipe_A2toT2);
        pipe(pipe_T1toR);
        pipe(pipe_T2toR);

        if (!(pid_A1 = fork())) {
                long read = 0;
                size_t size = 0;
                char *input_str = NULL;
                close(pipe_RtoA1[1]);
                dup2(pipe_RtoA1[0], 0);

                read = getline(&input_str, &size, stdin);
                printf("A1 : %s\n", input_str);
        } else if (!(pid_A2 = fork())) {
                long read = 0;
                size_t size = 0;
                char *input_str = NULL;
                close(pipe_RtoA2[1]);
                dup2(pipe_RtoA2[0], 0);

                read = getline(&input_str, &size, stdin);
                printf("A2 : %s\n", input_str);
        } else {
                FILE *fRtoA1 = NULL;
                FILE *fRtoA2 = NULL;
                fRtoA1 = fdopen(pipe_RtoA1[1], "w");
                fRtoA2 = fdopen(pipe_RtoA2[1], "w");
                close(pipe_RtoA1[0]);
                close(pipe_RtoA2[0]);
                fprintf(fRtoA1, "%s", file_paths);
                fprintf(fRtoA2, "%s", file_paths);
        }

}

I plan on having pipes to other processes, but now I just want to get the pipes from this program R to two other programs A1 and A2 working.

Program R will send file_paths do the pipes and A1 and A2 will print them.