Haven't read through the various responses yet, but here's mine before reading the others:

First, I think the $25 tables are bad for bluffing anyway. I won't say "never" there, but I'd be VERY sparing. I think that's a game to nut-peddle at.

Now as to hand 1: I don't like it in principle. I think the main key to a good bluff is that you've represented all the way through the hand exactly what they fear. For example (not meaning to harp on this one, but it's clearly my most successful PLO bluff), board is something like K65ss, which seems to be my favorite example board for some reason, but it's nice in that it's fairly rich in terms of draws. I bet out either flush draw or straight draw or both in LP. This works much better on checks or passive bets here, as full pot here, at least online, usually means one set or the other. This line is far more successful after a check-call from EP or MP or passive bet, call my pot-sized raise.

Anyhow, the board pairs on the turn, and it's checked to me. I'll effectively always now bet out half pot at this point, and I figure I have here well over 80% fold equity in the scenario outlined. I might refrain against completely moronic calling stations, but a drawing hand simply cannot proceed at that point against a very clearly represented full.

So, the reason I don't like the bluff on hand 1 is that the hand you're attempting to represent is a backdoor flush. Ok, you could have it, but it's purely random whether you do or don't, hence purely random whether they'll call or not. By contrast, if the river was a 4, then, yes, by all means, bet whatever represents your full (for me, I always bet half-pot on that one, and my bluff is exactly the same). But you've repped 99 here all the way through. You indicated you were scared of the straight on the turn--accurately, too, because it completely screws your straight draw.

I really think a good bluff has to rely on clear representation of the particular hand which now appears scary. The way you play it, it feels more to me like a last-ditch effort to salvage this pot on a board that's scary where you more than likely actually don't have it but might have stumbled into it.

I'll check out the other hands as well as comments later. Must run for now.