The siding quote and window quote look perfectly reasonable in separate emails. The trouble starts where both trades draw a line around the same piece of trim.
Name the type of window replacement
The Vinyl Siding Institute manual directs installers to the appropriate window and flashing details. Ask whether the proposed work replaces the full frame or retains parts of the existing assembly. Those are different access and water-management decisions, not interchangeable labels.
Give one drawing to both trades
Resolve the opening, flashing integration, wall repairs, insulation details, and finished trim before ordering. If the projects must be staged, ask what will need reopening later and who will perform it. Walk around each opening together and mark which trim is staying, which is being replaced, and who repairs any soft material uncovered. Photograph the agreed detail before siding hides it. Two estimates can both exclude the same strip of work without either total looking suspicious. Avoid choosing the schedule solely by whichever product arrives first. Include temporary weather protection while the wall is open.
Before the next step
- Confirm full-frame versus insert replacement scope.
- Have both trades agree on the flashing and trim connection.
- Document temporary protection and any planned future reopening.
Get the shared flashing, trim, and repair responsibilities into both scopes before either crew starts. When the wall is open, nobody should be discovering that the other quote was supposed to cover it.