Struggling to micro armies so that I can counter specific troops?

I’m playing against moderate AI, I improved my economy and macro (still got a lot to improve, but considering I watched 2 hours worth of videos I saw a massive improvement) but now I struggle with a. Pushing castles which are defended by many troops b. Fighting groups of various troops, even when I have counters for every one of them (I.e. they have Arambai, LSM and pikemen and skirms, I have mass skirms, Byzantine special unit (forgot the name) and some arbalests).

I struggle with some other things (I.e. reacting to getting attacked -> I just move my villagers to run away from it), reorganising villagers after garrison, but the one I mentioned is my biggest problem.

I managed to destroy two castles but my troops always died, it was pretty much stalemate and going no where for 15-20 mins (this was all that was happening, just rinse and repeat), and I was getting next to no where, so I just quit.

Any tips?