Hi @Rrrrrr and welcome to the community! One way of accomplishing what you ask is using RStudio Package Manager. Among other things, Package Manager allows you to easily host internal R packages alongside CRAN published packages. This allows users to install the internal package just as they would any other package using install.packages().
It's worth noting that Package Manager is a paid, enterprise product. If you're interested in a non-commercial solution, this thread has some alternative suggestions from the community.