Yeah exactly like you said, trying to “play” with us, the mom isn’t bad alone you just can’t pet her but if you get tough with her you get your way, the bullock is very lively and he is the actual danger.He has learned to be boss. When you say aggressive do you mean very lively as many bullocks his age will run towards you and can cause damage by what they regard as playing.
If it or the cow is actually aggressive and you can't walk in the field then that is as much a danger to others who don't realise. A cow may be excused a few days of protective behaviour but not 10 months.
Plenty farmers have found injuries hard to defend in court if a cow has already caused problems.
As above, get the bullock sold before it gets any bigger and find a quiet cow. There are thousands to choose from.
And find a friendly farmer neighbour to help you. Cows sold on their own are usually for a reason. Go to a herd dispersal sale instead