I was wondering if tracking devices/enchantments could be made. They would be given to guild members so the guild could keep track of their mission progress, and help if they're in trouble.
The item Crystal Ball
From the DMG (159), emphasis mine.
The typical crystal ball, a very rare item, is about 6 inches in diameter. While touching it, you can cast the scrying spell (save DC 17) with it.
The scrying spell on PHB (273), emphasis mine.
You can see and hear a particular creature you choose that is on the same plane of existence as you. The target must make a Wisdom saving throw, which is modified by how well you know the target and the sort of physical connection you have to it. If a target knows you’re casting this spell, it can fail the saving throw voluntarily if it wants to be observed.
You can use this item to spy on your guildmates as long as the NPC keeps touching the ball.
A Warlock alternative.
As an alternative, if you want a more automatic response you can, instead of using a super rare item, create a NPC level 3 warlock. A warlock 3 with Pact of the Chain and Voice of the Chain Master can maintain a group and the Warlock always communicated. The familiar "spy" can deliver information as long as they are in the same plane of existence.
Voice of the Chain Master (PHB 111)
You can communicate telepathically with your familiar and perceive through your familiar’s senses as long as you are on the same plane of existence.
If homebrewing is an alternative, you can create almost any magical item that your campaign needs. Being for thematically reasons or as a way to solve a particular problem, there is nothing in the rules that stops you (if you are the DM) to adjust as needed.
Retracting a decision
As the DM you have all the rights to retract a decision on your games. If a change suddenly seems more powerful than expected and its ruining everyone game, you can always take it back.