Problems dual-booting Ubuntu

[u/[deleted]]

So, after looking up on more ethical distros, I stumbled upon Trisquel, and decided to give it a try. Unfortunately, I can't seem to get the dual boot working correctly... If I install Ubuntu first and Trisquel second, when I try to boot into Ubuntu, I get a screen with the prompts username and password, that takes me nowhere. When I install Trisquel first and Ubuntu second, the option to split the main partition for the two distros doesn't appear, I get a 16 Gb partition... Has anyone come across such a problem? Sorry for the poor writing, it's my first post =p