They are indeed all silver; the 2 annas and the rupees are .917 fine, the quarter-rupees are .500 fine.
The mintmarks on coins of British India aren't as simple and straightforward as the mintmarks on American coins.
The two annas has two mintmark vaieties: B for Bombay and no mintmark for Calcutta on these coins, the "B" is "on the stem of the top flower".
The quarter-rupees: 1942 only has one mintmark variety, "no mintmark" for Calcutta. 1943 has three mintmarks: none (Calcutta), dot (Bombay) and L (Lahore).
The rupees: 1904 and 1907 both have two: none (Calcutta) and "B in the space below the cross on the crown" (Bombay). 1913 and 1918 also have two mintmarks: none (Calcutta) and dot (Bombay).
In all these cases, this is purely of academic interest; the mintmarks all have the same catalogue values.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis