First, let's start with your example sentences, because you aren't saying what you think you are saying...
Loosely translates to:
Thank you for letting me do A, and thank you for doing B.
As has been pointed out in one of the comments below your post, using the causative form + itadaku results in a 'letting (speaker) verb' construction. Here's why, the causative form of the verb (～させる) is a form for either 'letting' or 'making' someone verb. いただく is a verb for the speaker to receive something from someone else. When you say ～させていただく, you are literally receiving of someone letting the speaker (verb).
This is not the case for ～していただく which is where the speaker receives of the other person verbing.
There are a few cases where the causative form can be used, like the verb 話す. However, in that case, you are still humbly receiving of their letting you talk (to/with them). The only reason this can work is because 話す implies speaking with the other person. In cases of using keigo, you can also use verbs in which someone else gives to the speaker, like くださる.
You are right to point out that it is repetitive, because it is. That's just how keigo can go sometimes.
You can link the two different ideas/phrases by using the て conjugation. Another alternative is to use some other conjunctive form, and then using そして or また for the next idea. Also, because this is keigo, it isn't a bad idea to make sure that you acknowledge the time that the spent doing that thing for you.
After talking briefly with some Japanese friends そして is not as common as また. Also, their examples all showed that いただく and くださる are repeated for each of the tasks being performed. (Thanks @Chocolate!)
Thank you for doing A and B.
If you were a business executive (CEO or vice president level) meeting with regular staff, you may hear くれる. Neglecting this edge case, I would always recommend using the honorific in keigo.
As has been noted by others, you may not want to combine two things into one sentence when thanking. Keigo is round about enough that giving each thing its own sentence and recognition is in itself part of the formality. That being said, if I were to combine the actions in your example sentence, I would say the following (with special recognition from those that have helped me reach this conclusion):
Thank you for meeting with me and updating the schedule.