There are solo endings for each of the three characters, but it's also possible to have them all.
Viewing post in Sileo 0.59 Updates Now Available! comments
We've planned the route with two three-person endings in mind, however we're not outright committing to them at this stage as not to overload ourselves. Whether we include these paths will be assessed closer to the time they break off from the existing route and will be decided based on how development on that route has been going so far as well as how much interest people have for those specific possibilities.