Hi Fiona,
Welcome to the forum!
Generally the mixture of cultures that you will want will not be a 1:1 ratio, nor are they that way in the premix packages. Each company has its own "secret formula" for exactly how much of each they blend, but as a general rule, there will be a primary culture, generally either mesophilic (LL) or thermophilic (ST), and smaller amounts of various adjuncts that add additional flavor / aroma characteristics.
One of the most helpful books that I have found is Gianaclis Caldwell's
Mastering Artisan Cheesemaking; one of the things that makes it helpful is that she includes charts that suggest how much of the adjunct cultures should be added to go with the primary culture. For example, she suggests that LH should generally be used at a rate of 10%-50% of the amount of ST used.
Don't be too concerned about getting the culture to match exactly to the Feta B. In broad terms, the main thing to worry about is starting with the appropriate base culture, either mesophilic (generally LL+LC) or thermophilic (ST); from there you can experiment with different adjuncts to add different dimensions of flavor -- that is part of the fun of making cheese at home! If you are thinking, "But I want to make it the
right way" -- well, according to Caldwell, there are half a dozen different combinations of cultures that are appropriate for making Feta; all start with a mesophilic base (LL+LC), but some of the choices add only other mesophilic aroma adjuncts, e.g. Flora Danica Meso Aroma B, while others add one or more thermos, including a culture often used for cheddars (MA4000, LL+LC+LD+ST) as well as the Feta A/B mixture that you mention.
So, here's a couple of specific recommendations: For the hard cheese, start with the recommended dosage from the package of the ST, and then add to it half as much of the LH. For the Feta, go with your option 2, but use the recommended dosage from the package of the MA, then add a quarter as much of each of the others. OR use the recommended dosage of the MA, then add an eighth as much of the plain ST and LH that you were talking about for the hard cheese.
I have no idea if these recommendations are what anyone else would suggest ... but I am confident that, provided the rest of the make is correct, you will get cheeses that are at least in the ball park of what you are looking for. Start experimenting from there, and quickly you will build your own sense of what you like to add to various sorts of cheeses.
If you are in a position to do so, I highly recommend not only the Caldwell book, but also a pH meter -- the latter is a new-fangled invention in the ancient history of cheesemaking, but it surely does help those of us who lack decades of experience in knowing just the right moment to stop cheddaring, start brining, etc.
