Ahhh i love these! The structure, the way they kinda tie together, and the single story they can combine to paint <3
The 50 words and 100 words also tying the number into the story, had me puzzling on how you might have hidden 250 in the first one!

250:
This is a great little story, it's concise, and carries easily. You ease the reveal in slowly, so that instead of a wham-bam twist, its a slow build, where the reader wonders more and more. The real crux, the beauty in this one, is the unwritten, the space between the lines, and this is something I say to people from time to time, and can often mean that a story lacked conclusion, or something to give it a definitive edge, but that is not the case at all here, you have really nailed the snapshot, so as not to leave the reader cursing you for a cropped image, but wondering about the rest of the world, what has led to this state of affairs, where blood is so cheap, where did walmart get it, a lot of reflections on the value of life, the way its viewed as a commodity by some, and for something as life saving as blood to be sold at the supermarket. You could've used the tag speculative-fiction for this. The way that Bob is expecting the blood, clearly, he is waiting for it, but then, seeing it all there in front of him, and his reaction, as though he thought the would be fine, but seeing it all, the reality. There is a lot of philosophy in these 250 words, not written, but evoked <3

100:
on it's own - this is just a really sweet story, and painted in full color with your beautiful description

melting to puddles of ooze

there is again a wealth of implication, but a lot more of the familiar and domestic. Stand alone, these feel like an elderly couple, a well established relationship, grown with room for each other, and accommodating affection
but! If these stories are in the same world... and the items on sale are blood, so very cheap, it completely changes this so beautifully, what was a sweet story takes a wicked twist, as this woman is so blase about the cheap price of blood, while her husband balked at the world he now lives in. Also changes how the characters feel, suddenly they seem younger, and Fred's reaction becomes that to the wider world, what had seemed amusing, becomes thought provoking depending on the setting. Skill that is ;)

50:
on it's own - a tale of mystery and speculation! What are they selling, why have they had this rush, what is going on? with plenty of room for personal projection, i wonder, i would love to see what ten or fifteen different people thought was going on. Could it be money laundering - only on the books? Could it be fraudulent sales? or just a brilliant boom?
but connected. well it is just the perfect final bit here, the woman, making all these sales, the rate they are going out, confirming should the price of blood go up, is it really supposed to be this cheap, we are shifting a lot of it... getting more...

These three kinda come together to create a naturally feeling vampire world, without you ever saying it. Bob - the vampire with a conscious who orders the blood and feels bad about it when he sees how much arrives, Carl - the realist vampire, already adjusted to the new world and keen to find his place in the new supply chain, Fred - a relic from another age who finds the lack of value on life incomprehensible and the modern world beyond him, Margaret - a modern vampire all to used to the constantly changing world around her, having sheltered her husband (yep, they can be married, just decided :p) and finally Sherry - a remaining human, who really should be more concerned at the amount of blood they are selling!