My EotE group consists of just two players, both of whom created tough-guy type characters focused on combat. It doesn't look like the group will be expanding soon either. My problem is that while they are both excellent at combat, certain utility skills are not going to be their forte.

My solution to this was to give them temporary access to allied NPCs that could perform some of these skill checks if necessary, but weren't strictly as powerful as player characters (A smuggler and an astromech droid, both Rival-class NPCs from the back of the core book). I like the idea of them building a retinue of allies, and while I encourage them to branch out their skills and do intend to build their future adventures to complement their strengths, it's been a good way to ensure that I don't have to lock them completely out of certain options because they're terrible at computers, or piloting, or whatever. Note, I've been using published and fan-made modules thus far.

However, should I need an NPC that I can't find a readily available template for, whether for this purpose or when I start creating my own adventures, what are some tips for designing one. Specifically, I need help building stat blocks. For their allies, I'm looking at rival-class NPCs most. Is there a guide somewhere on this? Any tips from you guys?

Just look at the stats in the book.

Most rivals tend to have 1 primary attribute and 2 supporting. The more well-round rivals tend to have 3 above average attributes.

Skill wise most tend to have their primary skill as 2 (occasionally 3), secondary skills as 1-2 and tertiary skills as 1