  I have here, Terrine de Campagne and Mousse de Canard with Expiry of Mar 16, this year. Mousse de Foie expired Mar 22. So all are expired and their packages have ballooned up. I'm wondering if they are still safe to eat? 
I'm sorry to say that your three packages are no longer safe for consumption. Expiry dates are usually pretty conservative and food may still be good several days past them, but the concerning factor in your case is the ballooning of your packaging.  As various bacteria live their lives, they produce gas. A small amount of bacteria over a short amount a time will not be enough to produce enough gas to make any noticeable change to a packaging and is completely safe. However, the fact that your unopened factory-sealed packages have ballooned up points to a serious multiplication of said bacteria.    I recommend you throw away all three packages.  