DND 5E Eldritch Knight – Can an Eldritch Knight’s Weapon Bond Be Broken?

Yes, there's nothing (in the rules, anyway) preventing multiple Eldritch Knights from bonding with a single weapon.

Once you have bonded a weapon to yourself, you can’t be disarmed of that weapon unless you are incapacitated. If it is on the same plane of existence, you can summon that weapon as a bonus action on your turn, causing it to teleport instantly to your hand.

You can have up to two bonded weapons, but can summon only one at a time with your bonus action. If you attempt to bond with a third weapon, you must break the bond with one of the other two.

However, if the weapon is a magic weapon that requires attunement, only one person can be attuned to it.

As for breaking someone else's bond with a weapon, this is probably only possible with a well-worded Wish. Dispel Magic is the go-to spell for getting rid of annoying magic, but it only works on ongoing spells, which the bond clearly isn't:

At 3rd level, you learn a ritual that creates a magical bond between yourself and one weapon. You perform the ritual over the course of 1 hour, which can be done during a short rest. The weapon must be within your reach throughout the ritual, at the conclusion of which you touch the weapon and forge the bond.

Similarly, the bond isn't a curse, so Remove Curse won't help. You can render the bond useless by being on a different plane of existence to the Eldritch Knight, or being in an Antimagic Field. On the bright side, depending on how your DM interprets the phrase "you can't be disarmed of that weapon", it might be impossible for the other Eldritch Knight to summon it while you're holding it.

The co-operating knights can take turns to use it, but again, depending on how your DM interprets the phrase "you can't be disarmed of that weapon", they might need to drop it at the end of their turns so that it can be summoned by the other knight. Even if they don't have to do this, they're still going to have problems making opportunity attacks, since only one of them will actually be holding a weapon at any given time.

This is one of those situations that the rules don't really cover and as such would be left up to the decision of the DM.

Personally, I'd allow it for the sheer amusement of the player(s) but it would very much depend on what exactly is being used as the improvised weapon.

From the Improvised Weapons section on page 147 of the PHB:

In many cases, an improvised weapon is similar to an actual weapon and can be treated as such. For example, a table leg is akin to a club.

By this statement a DM could definitely treat objects similar to actual weapons as weapons for the purpose of a weapon bond.

However, the Improvised Weapons section also says:

An improvised weapon includes any object you can wield in one or two hands, such as broken glass, a table leg, a frying pan, a wagon wheel, or a dead goblin.

By this statement the players could find a lot of things that wouldn't fall within the "similar to actual weapons" clause and allowing "any object you can wield with one or two hands" to be subject to the rules of the weapon bond could create some pretty hairy situations.

As such I would allow improvised weapons to be bonded but would restrict it to objects that are similar to actual weapons and "common place" objects.

Also, this isn't defined within the rules but I see improvised weapons as just that, improvised, makeshift, and temporary. They are objects that wouldn't normally be classified as weapons except for under certain circumstances. As such it would be reasonable to say that Weapon Bond wouldn't work with improvised weapons because they aren't normally classified as weapons.