Can 2 or more players post their missed blinds at the start of a hand, when they’re not in the blinds but in middle position rather?

Sure, why not?

Typically yes, can't imagine a rule not allowing for this to happen. I've seen hands with three Players posting (plus the blinds) due to a rush to the buffet!!

The top two cases where this wouldn't be allowed IMO ...
1) A Player typically can't post back in on the Button, although if a Button straddle is allowed in that room there is a crack in that door by having the Player straddle as well as posting the dead SB in the middle. This is a rare spot since the Button would have to be moving into a dead spot to begin with.

2) Two Players can't 'buy the Button' side by side since it will be a mess in the next hand. (They both can't be the Button in the next hand.) One of the two Players must sit out a hand and depending on which Player sits out will determine the two possible spots in the next hand. One, if the first Player posts the second Player may now BTB (or wait another hand for the Button to pass) with the first Player now on the Button. Or if the second Player posted the first Player can now post behind the Button, with the second Player now being on the Button.

Typically, if allowed, an UTG Player can straddle and 'not' post any dead money in the middle to get back in the game.

All of these are room dependent of course, but to OP's actual question it's a VERY high percentage leaning towards yes, allowed. GL

Funny this came up. Last week I had the pleasure of being UTG for four hands in a row due to players returning and posting in a full ring game. None of us (including a very experienced dealer) had ever seen that before.

They can, but they are usually costing themselves money by doing so. (It's a bit silly to pay 1bb or 1.5bb to be dealt in if you're in a position where you'd usually only play 20% of hands or less. About 80% of the time you get dealt an unprofitable hand, so you'd rather not have to pay for the privilege). One reason someone might choose to pay is that they might have to wait 15 minutes before they are in the BB, as live games are soooo slooooowww.

Did you C-straddle?

Might depend on comps and timed promotions too.

The majority of people play live poker for entertainment and do not want to wait until the BB reaches them. Every time somebody sits down in MP or later and tells the dealer he’s going to wait for the big blind, I think to myself “great, another nit”.

As infrequently as I get to play, I am not going to "save" posting my blinds and watch multiple hands until the BB gets around to me.

I won't watch one hand either - I will "buy the button" because after one hand I have to post the same amount AND i won't have the button either. As I see it, buying the button gets two hands for free.

Will I watch TWO hands? If the game is really nitty, I can do that.

IMO.