Okay, the first thing to do is to publish the data to a different topic to the one that the publishing device is subscribed to.
Then, ensure that only Node-Red is “subscribed” to that topic (Node-Red has an MQTT In node listening g to this new topic). Your other Wemos device must not be subscribed to this new topic at this stage.
The other test to do is to publish a value to the new topic using MQTT Explorer (download link towards the end of this post)…
This published value should be received by Node-Red, and you should also be able to see values coming from the Wemos in MQTT Explorer.
Are you using Mosquitto version 2.x ?
If so, have you set your configured to allow anonymous access using listener 1883, as this could prevent Node-Red from seeing the messages from your devices.
Pete.