Your questions are pretty general, too general to be able to get an adequate answer here. Some guidebook research would serve you well.
Both American and United fly to Nicaragua and Guatemala. You could use either to book one-way flights to/from the US. Avianca and Copa connect MGA with GUA. Since those are Star Alliance airlines, you'd need to use United miles to book that flight. But February isn't far off. Would there still be availability? You'll have to do some digging.