so just kill him the usual way (but it will take longer as he blocks all the time as well!). when everyone else is dead its just you and the dad. you can kill the blue guys the usual way but they frequently block so just wait until they stop. don't try to get the dad during this because he will just block your moves and then one of the other guys will get you.
so, make sure all the red guards are gone and then take out the blue ones.
but you CANNOT run up the blue guards as they will knock you down and take a good bit off your health. the best way to kill the red lads is to run up them and attack, you do that by pressing X and then square and then of course triangle to finish him off (this will also work for you throughout the rest of the game). this part can be difficult as there are tones of fellow's besides his dad trying to get you and you cant freeze them to get more health! so, the easiest thing to do on the second you get in there BLOCK! and wait until one of them is vulnerable (but don't just stand there! walk around). There's a part in the game when you have to fight the prince's dad.