Yes Orendi is super fun. She’s a good match for most characters.
Boldur is definitely an acquired taste. You have to like that type of character which for the majority their tastes are for attackers because it feels like you’re doing more when you kill and do lots of damage.
Orendi + Oscar Mike would be a great pair. My husband and I run this team a lot. This is basically a heavy attack and AOE combo. Which is good. Attackers really stand out in this game and both of these characters have a low learning curve but can be very versatile once mastered (not the title but whenever you get a full understanding of all the possibilities these characters have. Same goes for all characters really). Like with Caldarius + Rath, focus on one character when able and just shoot and throw down your AOE on them and knock out minions quick. Attacking sentries will be super easy. Depending on the other characters that are on your team, you guys should be able to get in some good hits on the sentry without being hurt by other players (watch out for the sentry’s attacks) and then back out quick before you get too low on health. Lots of pushes and comebacks come from dying at the enemy sentry and the opposing team rushing into your territory while your team respawns. Ditto for your team; take this opportunity if you have a full team, or at least 4 players alive, to rush the enemy sentry.
Other great match ups would be Oscar Mike + Galilea, Orendi + Galilea, Montana + Oscar Mike, Orendi + Alani, Orendi + Deande.
Once you find your favourite characters you will find different combinations that work well for both of your playstyles.
Couch co-op is definitely the best 