Don
Never hesitate to ask a question or to ask for clarification here. We are glad for the opportunity to be of assistance.
What you are encountering when you go to add to an existing Timeline is to be expected unless....
Hold down the Alt key of the computer main keyboard as you drag the file into place on the existing Timeline. This maneuver
will avoid disturbances to the existing Timeline.
Sometimes if you want to keep a group of clips under control as you make your moves and changes, you can select all the clips for the
group and then use the Group command on them. Thereafter the group will move as a group. See Clip Menu/Group and Ungroup commands.
Premiere Elements does not have a locked track feature.
Practice selecting a group of clips all at one time by drawing a rectangle with the mouse cursor from the top right edge of a group of clips diagonally downward to the lower left of the group.
You might find this free video tutorial on "keyboard modifiers" interesting in this regard.
Premiere Elements: Arranging clips on the Timeline using modifier keys | lynda.com - YouTube
It is provided for informational rather than promotional purposes.
Please review and then let us know the outcome.
Thank you.
ATR