Вы можете попробовать это:
this.loginForm = this.formBulder.group({
'fname': new FormControl('',Validators.required),
'lname': new FormControl('',Validators.required),
'email': new FormControl('',[Validators.required,Validators.email]),
'password': new FormControl('',[Validators.required,Validators.maxLength(5)]),
'retypepassword': new FormControl('',[Validators.required,Validators.maxLength(5)]),
});