Is there a workaround for using 1 iMessage account on multiple iphones?

I use iMessage on all of my devices. That includes my watch, iPhone 12, iMac, and iPad. It also includes two other older iphones. I'm able to send and receive texts over iMessage and over SMS that all sync, EXCEPT for the two older iphones.

The problem is that even though the two older iphones are signed in just fine, i can only receive, but not send SMS messages. I assume that it's in the way the iPhone is developed to be the main device on iMessage when it comes to SMS messages? But is it possible to use them to send and receive SMSs going back to the main iPhone(12)?