This should be an easy one, if you dont currently see a PARENT column in your timeline then right click in the empty space next to source name. There you will see an option to add columns. add the PARENTING column and AFTER setting the base size and position of your 2 layers parent 1 layer to the other. Then only adjust the position, scale, rotations etc on the layer that you have designated to be the parent.
You can parent one layer to the next by either selecting the layer in the drop down list or selecting the pick whip (the curly icon next to the drop down list) and drag that to the layer you want to parent too.