[RPG] Meld Into Stone would fail if I have living spell components in the pouch

A sprig of mistletoe is a sprig of mistletoe

The druid requires a sprig of mistletoe to cast his spells, which is defined in the equipment section as costing 1 gp. It's not defined anywhere as a specially blessed sprig of mistletoe or anything. You can, rules-as-written, use any sprig of mistletoe as your spellcasting focus (unless the DM rules that it must be specially harvested mistletoe or the like).

Being a sprig of mistletoe, it also meets the prerequisite for the material component for goodberry. Note that spell components are not consumed unless the spell says so.

However, there's no reason a wizard's spell component pouch would automatically contain every possible spell component for spells the wizard doesn't have, such as a sprig of mistletoe for the druid.

Rules-as-written, in chapter 10 it states that a spell component pouch can be used in place of the actual material components when casting a spell. This means the druid can technically borrow the wizard's pouch and use it in place of his mistletoe. But there's nothing in the rules which says you can take components out separately. You cast with a focus, a material component, or a component pouch, but no rule says you can divide a pouch up among the party and still have it act as a pouch.

On the other hand, as per chapter 5, a component pouch is nothing more than an empty belt pouch "to hold all the material components and other special items you need to cast your spells". The wizard's spell component pouch is nothing more than a belt pouch he uses to keep his spell components for his spells, not every possible spell component. From the realism standpoint, then, you can't take his mistletoe unless one of his spells requires mistletoe.

In short, all mistletoe is mistletoe, but you can't take one from your wizard's spell component pouch because if you're being realistic, he doesn't have any mistletoe, and if you are being rules-strict, you can't separate mistletoe from the pouch.

No. Meld into stone targets the stone, and allows the caster to meld into it.

The range of the meld into stone spell is listed as "Touch".

The description states, in part:

You step into a stone object or surface large enough to fully contain your body, melding yourself and all the equipment you carry with the stone for the duration. Using your movement, you step into the stone at a point you can touch. Nothing of your presence remains visible or otherwise detectable by nonmagical senses.

As you can see, the entire spell description (which continues beyond this) repeatedly refers to "you", not "a creature" or "another creature". It unambiguously targets a stone object or surface and affects the caster; at no point can another creature be targeted by the spell.

This is supported by this unofficial tweet from January 2018 by rules designer Jeremy Crawford:

Hey! Question can you target an enemy with the spell Meld into Stone? Example: pushing them into a wall of a dungeon. If so how would you rule it?

Meld into Stone affects only the caster and the stone the caster touches. If a spell allows you to target others, it defines for you whom you can target.