First off it depends on whose names the contracts are in
secondly buying things for someone else don't tend to be covered as S75 is a thing for the card holder personally. The wedding reception and the dress are not for you so your claim would most likely be rejected.
Section 75 does apply in circumstances where a person buys goods or services which they
then gift to another. But that is where they have an agreement with the supplier to acquire
the goods or services and they then gift them to another.
New plans have just been announced by the Government
DON'T assume your landlord covers you
Incl £2ish sun cream & £1.50 disposable BBQs