Hi, cel70. Welcome to go!
You have gotten some good advice. Let me just add a comment or two.
You are having trouble telling which stones are alive or dead. That is normal for a beginner. And let me assure you that even players much stronger than you sometimes have that kind of problem, too. Usually because they think that some stones are alive that can be killed or captured.
The good news is that it won't take too long before you will be able to tell which stones are alive or dead at the end of the game with great accuracy. For now, you should just play on until the status of every stone seems clear to you. And make sure that all the dame are filled, except in seki, OC.
Doing so may cost you some points by Japanese (territory) scoring, but learning to tell which stones are dead is more important. If that bothers you, you can play by Chinese (area) scoring.
Let me illustrate with your last diagram. I suppose that it is Black's turn, either because White just passed, or because Black has captured one White stone. There are still dame on the board.
(;FF[4]AP[GOWrite:2.3.46]CA[ISO8859-1]ST[2]GM[1]SZ[9]PB[ ]PW[ ]PM[2]GN[ ]AB[af][ag][bg][cg][cf][ce][be][bd][ca][da][db][dc][fc][fd][gd][hd][hc][hb][dg][dh][di][eg][fg][gg][gf]C[Let's start in the top right corner, because you think that the Black stones there might be alive. If so, there is still territory to make there, and dame to fill.]FG[259:]AW[bi][ba][ad][bc][cc][cb][cd][ec][eb][fb][gb][gc][de][ef][fe][ge][he][id][hf][hg][gh][fh][eh][ei]
(
;C[Threatens to connect to the Black stones and capture the five White stones.
See variation after you have explored this line.]B[ed]
;W[dd]
;C[Threatens to capture the White stone.]B[ic]
;C[White does not care.]W[ac]
;B[ga]
;W[df]
;B[ie]
;W[ff]
;B[if]
;W[ae]
;B[hh]
;W[hi]
;B[ig]
;W[ih]
;B[id]
;W[ah]
;B[bh]
;W[ci]
;B[fa]
;W[ea]
;B[ha]
;C[Maybe now it is clear that the Black stones on the right are dead. But what about the bottom right corner? Black has an eye, but there is a ko. ]W[tt]
(
;C[See variation after playing out this line.]B[ai]
;C[White has no threat.]W[tt]
;C[Black wins.]B[ch]
)
(
;C[If White "wins" the ko.]W[ai]
;C[It does not matter. Black is alive and White is dead.]B[ch]
)
)
(
;C[We know that the Black stones in the top are dead, as is the White stone in the bottom left. But this is a dame.]B[ae]
;W[ac]
;B[ff]
(
;C[After you have explored this line, come back and see the variation.]W[df]
;B[dd]
;W[ee]
;B[ed]
;C[Makes two eyes.]W[ab]
;B[ie]
(
;C[After you have explored this line, come back and see the variation.]W[hh]
;B[ic]
;W[if]
(
;C[After exploring this line, come back asd see the variation.]B[ga]
;W[id]
;C[Black has no ko threat.]B[tt]
;C[I think you can score the game now.]W[ie]
)
(
;B[id]
;C[Prevents Black from making an easy eye here.]W[ha]
;B[ea]
(
;C[After exploring this line, come back and see the variation.]W[ga]
(
;C[Seki. I think that you can score the game. See variation.]B[ib]
)
(
;C[Ko.]B[ia]
;C[But Black has no ko threat. Big loss for Black.]W[ib]
)
)
(
;W[ia]
;B[fa]
;W[ga]
;B[ib]
)
)
)
(
;C[Capcures a stone, but . . . .]W[if]
;B[hh]
(
;C[See variation later.]W[hi]
;B[ih]
;W[ha]
(
;C[After exploring this line, come back and see the variation.]B[ic]
;W[ea]
;C[Big ko, but White has no threat. ]B[ie]
;W[tt]
;C[I think that you can score the game.]B[ig]
)
(
;B[ib]
(
;C[Threatens to make an eye here. See variation later.]W[ga]
;C[Captures the four White stones.]B[gi]
;W[fi]
;B[gi]
;C[Makes the eye, but these stones are dead. Can you see why?]W[ea]
)
(
;C[Protects these stones for the moment.]W[gi]
;C[Not really necessary, as Black can make the same ko. . . .]B[ea]
;W[tt]
;B[ic]
;W[fa]
;C[Not necessary, but this way the ko is not big. In fact, . . .]B[ga]
;C[White cannot win the ko and the White stones are unquestionably dead.]W[ie]
)
)
)
(
;W[ih]
;B[hi]
;W[ha]
;C[All the White stones except those in the top left corner are dead. Can you see why?]B[ib]
)
)
)
(
;W[ee]
;B[df]
;W[tt]
;B[dd]
;W[ed]
;B[ab]
;W[ea]
)
)
)
at 1-2 would be another reason, why 
in the lecond variation is bad