Probability question (moved from General Betting)

I posted this in GB but no responses so thought it might be more appropriate here.

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Perhaps an easy one for some but I'd appreciate guidance.

Say I have a group (population) of horses that win a set of races (events). These horses have some things in common and I want to know what the probability is of this group winning this set of races. For now I will ignore the implied odds (the market) and assume they all horses have an equal chance in all races.

Let's say the groups/runners are as follows:

Race 1: 5 of 18 runners
Race 2: 6 of 20 runners
Race 3: 5 of 17 runners
Race 4: 7 of 19 runners
Race 5: 6 of 18 runners

All races are independent of each other of course.

So, my approach is the probability of the group winning the first race is 5/18 = 27.8% or 3.6/1...is that correct?

And for all it would be 5/18 x 6/20 x 5/17 x 7/19 x 6/18 = 0.30%...but I'm not sure about this.

Alternatively, if I know that this group of 29 runners have won 100% of the races, what does that tell me in probability terms?

Also meant to say, what can I deduce from the total qualifying population i.e. 29 producing all the winners from a total population of 92 runners?

That equals 31.5% but not sure if that is meaningless.