Confused by the Term "Welfare Relative to Full Information Welfare"
What it means is the following:

Consider the same bargaining game played by two players that are fully informed (i.e. the buyer is also informed about the value of $q$). Then find the equilibrium of this game and calculate welfare. This is the ``full information welfare'' that the question refers to.

Then solve the model where only the seller is informed about the value of $q$ i.e. find the equilibrium of this game. Now calculate equilibrium welfare. How does it compare to the one you calculated for the full-information case? I would probably do this by calculating the fraction
$$\frac{\text{Asymmetric info welfare}}{\text{Full info welfare}}.$$

Lastly, you need to see how this fraction changes as the values of $\alpha$ and $\delta$ change.