Here's my answers (whited out) - they may not be 100% so I want be put off if someone wants to correct.
1. What does redbl show in these auctions :-
a. 1-dbl-redbl
A redbl here shows 10+ hcp and implies no fit. After this redbl your side holds the balance of power so you either win the auction or double the opps for penalty.
b. 1-dbl-pass-pass-redbl
The 2nd pass indicates a willingness to penalise the opener. So here the redbl is 'help' or SOS (for example the 1d opener was a 4-4-3-2 hand)
c. 1-pass-pass-dbl-redbl
The dbl here is balancing - unlike 1b. there has been no penalty pass - the redbl here says 'I have extra strength - I am certainly making 1d xx'
d. 1-pass-2-dbl-redbl
A redbl by the opener after you have found a fit indicates extra values and a willingness to penalise the opps at the 3 level. It means all subsequent passes by your side are forcing.
e. 1-pass-2-pass-pass-dbl-redbl
A redbl by the responder after you have found a fit indicates extra defensive values and a willingness to double the opps. It means all subsequent passes by your side are forcing.
2. What does the final pass indicate in this auction (or is it forcing)?
a. 1-dbl-redbl-pass
The person in the 4th seat can't have much - if you take 12 for opener, 12 for double and 10 for redouble (all minimums) that leaves at most 8 - but usually less. This pass is never a willingness to penalise 1h. If you are the doubler with an ok hand and heart shortage dream on. This pass just denies any useful bid - its a bid which says 'your made your trouble partner - you're on your own'.
b. 1-dbl-redbl-1nt-pass
This pass is forcing. It does not mean minimum (in fact with a minimum offensive you will usually bid something) - it means some willingness to defend 1nt doubled and leave the decision to partner.
c. 1-dbl-pass-pass-redbl-pass
Partner has passed for penalty, opener has redbld for SOS - you're happy to go with penalty.
d. 1-pass-pass-dbl-redbl-pass
Partner has balanced and even though opener has redbld showing extra strength this pass says 'playing a diamond redbld contract is ok with me' - but it may take a brave balancer to leave it in!
e. 1-pass-2-dbl-redbl-3-pass
This pass is forcing - opener has indicated extra defensive values and an interest in penalising the opps at the 3 level. The pass says 'your decision partner'.