I struggled with my daughters tantrums because I really wanted her to behave in a certain way and in time I relaxed a bit, I feel sometimes tantrums need to kind of run their course and at the end the child needs to relax and not be overly punished for losing their cool.
If they are hitting or biting or breaking things then of course that will need to be addressed in some way, but if they are 'just' not complying with what you want them to do then in some ways I would relax a bit and just take it as situation you can't alter in the immediate future. So to some extent you need to kind of sit it out.
This is JUST my thoughts! Ignore me or seek wiser guidance.
I now have a part time job and my DD is in school so things like getting dressed and eating breakfast need to be done or the whole day grinds to a halt! But when a child is quite young, maybe 2, sometimes it is possible more to go at their pace, if you are not working outside the home and if school is not yet compulsory.
I know one of your DDs is 4 and not 2 but if she is not yet at compulsory school it is not such an issue if she gets dressed a bit later or eats breakfast a bit later.
Of course you do not want this to go on forever but if you can allow the schedule to be a bit more slow then that might help.
Personally, I would also try and pre-empt the tantrum by getting her involved in limited choices. So you could have two cereals, the tiger or the Gofer brand (or whatever - we tend to know the cereals by the animal on the box). Ask her to choose which of the two and to help you set the table for the three of you.
She can help because she is a big girl etc.
I agree not too many choices and as much as possible this is what we are doing but I would be relaxed about exactly when it happens.
It might also help if once she has complied with the getting dressed etc there is a trip to the park or walk in the garden to look for snails or whatever to look forward to!
I would also add that once the tantrum is over she may well want to hug you or she may want distance to cool off but once she is ready to come and hug you - be ready for her and if possible try not to allow it to sour how you feel. They are not fully in control in a tantrum so they might say hurtful things. I do think it is right to let kids know that the things they say are hurtful but it is best not to allow it to hurt you too much otherwise you may (as I did sometimes, to my shame, say mean things back because it can be hurtful to hear mean words and it is easy to reply in a mean way - I am sure you do not but I did!).
If your DD can count to 5 or 10, I'd also encourage her when she gets angry or starts to get angry a kind of take deep breaths and count to ten - the kind of thing to relax, it is very hard for a 2 year old and your 4 year old may not manage it but if she sees you doing it she just might catch on.
This might help her (or you) before the tantrum gets under way.
If you have tried all this please ignore me!
My tantrum days are (for the moment) behind me!
Just my thoughts, feel free to ignore.