What brand are these pex threaded T connectors?
These are actualy "Qest" (pronounced "quest") brand fittings that were more popular 10-15 years ago (maybe further back).  I remember in the early 2000's these were sold at Home Depot and Lowes back before they had very much PEX plumbing supplies.  They were common in mobile homes.

Here is a sample at a plumbing supply retailer:

https://www.ferguson.com/product/qest-plastic-compression-tee-assembly-qqat/_/A-ProdFamily-216224