I am not sure that I understand the translation.
1920 x 1080 50i is 1920 x 1080 @ 25 interlaced frames per second. That 50i represents 50 fields per second or 25 interlaced frames per second.
1920 x 1080p50 is 1920 x 1080 @ 50 progressive frames per second.
Are you asking how to get both those formats into one Premiere Elements project?
What version of Premiere Elements are you using and on what computer operating system is it running?
You realize that Premiere Elements (any version) allows for only one project preset. In that case, you set priorities and then fit the second into the other.
In this case, try setting the project preset for
then import the 1920 x 1080i25 and then 1920 x 1080p50. What is your intended export?
More considerations on this in the morning.