How to get texts from one contact's email and phone to show up in one message box iPhone?

One of my contacts can send me text messages from their phone and also iMessages from two different email addresses on their computer and iPad.

The problem is, even though all three are connected to the one contact, they show up as three different conversations, which is mildly annoying because I don't know which one is which when I open my messages and want to send a text, and also it makes it difficult to follow a conversation sometimes.

Is there a way I can make messages from all three show up as one conversation?

Not you, them. They have to be consistent in sending a thread by either email or phone number. If they would send you a text via email (to your phone number email address, not your name email address) so it shows up in texts and not your email inbox would be the easiest way. Best luck.