Is it true that these two descendant transactions will only be broadcasted and picked up by the miners when the ancestor is confirmed?
They will only be confirmed when the parent transaction is confirmed, either in the same block or in a preceding block. As the parent transaction isn't relayed, your subsequent orphan transactions can't be confirmed as well.
I tried to bump the fee for the first low-fee transaction by using bumpfee "tx-id", but that does not work as the transaction has descendants.
I do not have the luxury to just wait until they are removed from the mempool because the other two transactions should already have gone through yesterday.
None of your transactions are replaceable so bumpfee will not work regardless. It is not in the mempool in the first place, or at least its very poorly propagated. You can try scripting a raw transaction instead with the inputs used in that transaction. It'll go through just fine.
How to fix this? Is it still possible that I ask a miner or - as what was suggested in the "Stuck transaction topic" - to ask someone who has access to F2Pool's transaction selector?
I am willing to pay for the fees of course.
Below are is the output of the mempool entries of the three involved transactions
Possible. I'm not aware of anyone who has access to that though. Be wary of anyone claiming they do and attempting to collect payment upfront.