From what I understand you want the entire model to tween / move?
If you want to move an entire model use model:PivotTo(CFrame) where CFrame is the CFrame you are moving it to.
If you want to move everything inside the model with a tween make sure everything is welded to the PrimaryPart (you stated this), and use TweenService on the primarypart. Make sure everything other than the PrimaryPart is unanchored.
I tweening the player part but group model falling behind when I tween the part so I want to move it with player part. Can’t I just move it with welds with player part?
Do not tween the PlayerPart, tween the Model instead. Unanchor and weld everything inside the model to the model’s primary part (make sure the primary part is anchored). Then use something like this to tween the model:
local tweenserv = game:GetService("TweenService")
local tweeninf = TweenInfo.new(5, Enum.EasingStyle.Sine, Enum.EasingDirection.In)
local tween = tweenserv:Create(script.Parent.PrimaryPart, tweeninf, {Position = Vector3.new(Position Here)})
tween:Play()