How did Lord Capulet force the young ladies to dance with him?
I think that you are talking about the part in Act I, Scene 5 where the Capulets are holding the dance. This is the dance where Romeo first sees Juliet.
But I do not think that Lord Capulet is forcing the ladies to dance with him. He is, instead, making sure they dance with other people. What he says at the beginning of the dance is that every lady who does not have corns on her feet will dance. He then says that this means anyone who doesn't dance must have corns on her toes. The women will not want people to think this, so now they will be forced (in a good way) to dance.
Ah ha, my mistresses! which of you all
Will now deny to dance? She that makes dainty,
She, I'll swear, hath corns.
But Lord Capulet himself tells his cousin that they are too old to dance themselves.
Nay, sit, nay, sit, good cousin Capulet,
For you and I are past our dancing days.