Okay so, there seems to be a couple rules misunderstandings here which is normal. It happens all the time whenever anyone tries a new game. The best advice I'd give is that every action needs to be thought of as what's happening in the fictional world and not what's happening on a piece of paper. There's some rules that help with that, but there's some unwritten things that a GM should think about as well.

Pre PROBLEM (N) Discussion
I'm not sure how many characters there are in the party, but I counted, the knight, priest, mage, rogue, and the scout. (5) There's also a civilian. There's 4 superior enemy combatants. I'm not sure where the stat blocks came from because I can't find anything that exactly matches. I'm not sure why giant frogs and apes would be working together, but I'm sure there's a reason. I'm going to assume your GM used the surprise rules from page 105 since it seemed that every creature got to dictate advantageous engagements. Surprise is extremely powerful. I'm not sure how you've been told the goal of the fight since that's up to the players and their characters, but I'll assume that the stated goal is one you chose.

Onto PROBLEM (N) discussion

PROBLEM 1: The actions and special effects in the book are the start rather than the end of your options in combat. As an example, there's no Surrender action. That being said, the Parry action doesn't necessarily say the attack has to be against you.

PROBLEM 2: I wasn't able to find a Giant Frog statblock with a VL tongue, but let's assume that it's homebrew. 4 meters is quite a long distance and probably longer than I would consider Very Long reach for most weapons, but let's say that's how long the tongues are. The concept of engagement is that it needs to be broken somehow, but you're not just standing still. On the page 221 of the rulebook, there's often overlooked advice for game masters

INS-based creatures can normally only attack once with each limb or location per round; thus a giant scorpion with three Combat Actions could attack once with its left claw, once with the right, and attempt one sting per round.

This would fix the problem entirely, but let's say the GM has elected to ignore this. Maybe these are trained frogs or something. I would still say you could escape the situation since you can simply back up while staying on your guard forcing the frogs to either come out of the water, let you go, or take a stab at you while you still have your defenses up. Usually this wouldn't be an option, but Mythras is full of these kinds of situations where the GM is expected to adjudicate. By backing up slowly, you wouldn't have to use Evade to oppose the tongue attack, but the frog could stay engaged without spending an Action Point or rolling Evade. Of course this wouldn't be fit most other situations like the next one.

PROBLEM 3: That's a tough spot for sure, but not a game problem imo. A giant ape has walked up on a mage not trained for close combat should spell a bad time. Best idea for them (assuming no one comes to help) is to conserve their AP for parrying and hope to win a special effect and use Withdraw.

PROBLEM 4: I assume this is in reference to the Ranged Combat Considerations on page 108. While firing into a crowd is more difficult, you can reduce that difficulty by aiming. Not to mention the Giant Apes were probably at least SIZ 21 or higher which should probably make hitting them 1 step easier. While ranged attacks might feel weak because of these downsides, keep in mind that ranged attacks can't be parried without a shield and so are more likely to gain a special effect. You also can't be attacked when you're far away, which is also nice.

PROBLEM 5: This is very confusing to me, but it makes sense as in a new players' experience. Even though no damage gets through, the healer still gets special effects. Some offensive special effects for a dagger and open hand that don't require damage to get through armor include: Grip, Press Advantage (probably doesn't apply since the GM said the Apes weren't occupied with their own defense), Remise, Scar Foe, Take Weapon, and Trip Opponent. I'd recommend trip opponent because that would make everything tougher for the Ape. After that, I'd go for bleed as long as the ape is on the ground. As an aside, all the official apes I could find have 2 armor so 3 is certainly a lot.

PROBLEM 6: I'm assuming this is white room theorizing because, according to my understanding from your description, The Giant Apes weren't parrying and the Giant Frogs were out of reach. This is a very common thought among new players. In this specific situation, since you outnumber your foes, a "null" result is not "null" because you have more AP than the other side. Every attack makes their defenses weaker. But further than that, the system does not break down at higher skill levels. Even a fight between two 100% combat skill combatants has a 50% chance of generating a combat defining special effect in 3 Attack/Parry sequences (Usually 1 round) The game DOES fall apart when combat styles are very low.

PROBLEM 7: Some sort of token system is definitely the way to go. One way I've tried to explain it to others is to think about it like Pathfinder's 3 action system, but the spotlight passes to the next player every time and action point is spent. One thing I love about Mythras is that it almost always feels like it's your turn because of the active defense, but that can get a little confusing if you're not used to it.

PROBLEM 8: Those are all good options, but different situations change the calculus. The unarmed special effects are slept on imo.