trennels | A Few Things I Don't Understand

Can you help?

1. In Peter's Room, Peter, Rowan and Karen are in the bathroom. Peter draws 'an X on the surface of the water in the basin to avert a quarrel'. What does this mean?

2. In Run Away Home, during all the hoo-ha about Nick borrowing Ann's bike to go to Mass at the Merrick's, Rowan says, "I ought to warn you that when old Ramsay [I assume this is their local vicar] does his duty by the A.S.B first Sunday of the month, our mama cuts Matins and goes to evensong instead." What's ASB, why is Ramsay involved avd why would that make Mrs Marlow change her church-going habits?

thanks!