Split Form in Subform or same effect 2 subforms

Anyone know is it possible to have a split form in a subform?
Because if I created 2 subforms; 1st single form and 2nd Datasheet, and Set
the master child field the same but i cant get the same effect, when i select
the recordset on 2nd form(datasheet) the 1st Single form recordset din change
accordingly? May I know how to solve this?

or Is it possible to create a split form but have same effect with Main and
subform?

Example
in a combo box I select Customer = "ABC"
then all the transaction record for Customer "ABC" will come out in a Single
form and datasheet form but both link to Customer "ABC" and if I adding new
Transaction in either Single Form or Datasheet then the Record will automatic
adding Customer as "ABC" and when I clicked any record in Datasheet, the
Single Form should Changed to same record as I Selected in Datasheet.

Thanks,