Can I install my UE4 on 3 PC's?

The problem is quite simple. I bought sub on UE4 and installed it on my primary PC. However I would like to have it also on 2 other PC at my home which are in my gabinet and in basement lab??

Is it possible to just log in on those PC’s and just install it just like I did on my primary PC ?? There won’t be any problems ??

Yes its possible, as long as you are only user using it, it’s ok to do that

What is more. Can I be logged on 2 PCs info unreal engine at the same time or not?

As long as you are not sharing your account with others, yes.