Besides it would have been understandable if the unconfirmed tx was only the previous one, but they are creating a long chain of unconfirmed transactions and if one of the ancestors (like 6f06c23dd9...) uses RBF to bump the fee, the entire chain becomes invalid and they'll have to resend all of those transactions again manually.
It looks like there is no other way for OP to fix the thing but to wait until all the ancestor's transactions are confirmed. Considering the given scenario, RBF and CFNP won't help in this case without invalidating the latter transaction, Yes?
CPFP that spends any unspent outputs derived directly or indirectly from the unconfirmed outputs will not invalidate any transactions.
RBF on the final transaction can be used as CPFP. It will replace the original payment to the OP, and not invalidate any others (except successor transactions spending the unconfirmed coins).
Coingate.com has the ability to fix the problem, but they are willing to lose customers to save some money. It is unlikely that the 3 s/vb transaction will ever be confirmed, therefore waiting is not an option.