Okay so there is too much confusion here, between Summon, Contracts and Bijuus.
So I will start it with summoning contract. Summoning is basically a space time type ninjutsu.
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That is it instantly makes creatures from a separate space to appear in front of you.
Summoning needs you to sign the contract with the animal, that you wish to summon. Kurama on the other hand can't have summoning contract, as he is a bijuu and not a summon, since summons are the animals that are alike and reside at their own place.
Kurama isn't an animal, it is just a chakra beast.
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But then about the scans you mentioned, how can they perform summoning without contract?
That is due to the nature of summoning jutsu, that is it is a space time ninjutsu, which require seals and formula to perform, such as FTG. In this case, contract isn't there, because this isn't pure summoning, but a 'forced summoning' and hence Obito and Madara can perform summoning jutsu, because they know the formula or seal, which is same in both the cases(look at above scans). Just like summoning tatoos can be used to summon creatures. Contract is just a way to put it in a sophisticated way and make the process quick.
Although in latter case, Madara failed because dimension inside Naruto isn't accessible from 'outside', typically from large distance.
Now, what Minato did here?
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He simply freed Kurama from control, but didn't do something about contract, since there wasn't any contract, but just a formula, which Obito can remember and summon him again.
OT-Sasuke can't summon Kurama because he never got any info about how to do it.
He simply knows how to control Kurama, which is via genjutsu, but it is released now and hence Kurama isn't Sasuke's asset.