Following on from Nogithere‘s post, could anyone say whether anonymity is increased if each of the three mixes uses more than one server and, therefore, more than one IP?

Nogithere gave the example of the last mix in Luxemburg (in the France, Netherlands and Luxemburg chain) having three separate IP addresses.

Also, it seems that my internet provider uses the same three servers, e.g with IPs:
123.XXX.XXX.X
456.XXX.XXX.X
and
789.XXX.XXX.X
before my requests get to the Jondonym mixes. Does this help anonymity, or not.

I apologise if these questions seem facile, but I am a newbie, so I would be grateful for any help the community can give.

Thanks

Anonymity against whom?
Beginning with your second question: It does not increase your anonymity as both your ISP and the first mix know that it is the same user. If some independent third party is wiretapping, it would just see that somebody is connecting to the mix. Depending on its knowledge and the collaboration of the ISP and the first mix, the worst that can happen is that it knows that all three IPs belong to you.
Regarding the first question my answer is that chances are good that this setup decreases anonymity as not all users are using the same route which which makes them easier to distinguish.