I have started cultures off of slants that were several years old. The trick when starting an old culture is to start with a reduced amount of medium (wort) at a reduced gravity. In this case, I would pitch one package into 250ml of 1.020 wort. If one uses the metric system, making 1.020 wort is child's play because a 1.020 starter is a 5% w/v solution. We can make a 250ml 5% w/v solution by mixing 12.5 grams of spray malt into 250ml of water. At 5%, the sugar will not do much in the way to increase the volume of the solution because it breaks down into molecules that take up much less space. You can do a 250ml SNS starter in a 1L bottle or even a 1L Erlenmeyer flask if you use a sanitized solid stopper during the shake (you need to hold on to the stopper or it and the wort will go flying). I would wait for 12 and 18 hours before stepping it up it up to quart using 750ml of 1.040 wort (1.040 is a 10% w/v solution; therefore, you will 750 * 0.1 = 75 grams of spray malt to make the step up starter wort), what you want to do because the first-level starter is bound to have lot of dead cells is to only decant the supernatant (the liquid that is above the solids on the bottom of the container) into the next step wort. Whatever you do, do not allow the first level starter to ferment out because it will be much more difficult to separate the viable cells from the non-viable cells and you only want to pitch viable cells into the starter you plan to pitch when there are that many dead cells. I would use SNS for both steps. Remember, a huge part of SNS is pitching everything at high krausen; however, in the case of the first-level starter, you only want the cells that are in suspension. If you do it right, the only thing that will be on the bottom of your second-level starter well be break.
By the way, throw your yeast calculator away. Yeast cultures are like nuclear weapons because close is good enough. Yeast cells grow exponentially, not linearly, as many home brewers believe. The yeast biomass cell doubles every 90 minutes; therefore, the difference between 1L starter and a 2L starter is one replication period the starter is pitched. What is more important is pitching healthy cells at the right time. Another thing is that a lot of home brewers are afraid to do is to pitch starter wort believing that it will make their beer taste bad. That only occurs when one uses a stir plate due to the stress a stir plate places on the cells. If one smells an SNS starter at high krausen, it smells a lot like bread. That is because the cells have not experienced the stress that they experience on a stir plate. Stressed cells are not healthy cells.