Double vowels -- how to pronounce?

Latin
1

Here are some examples:

Tuum

filii(of the son)

manuum

Not able to type macrons.

So, my question is how are double vowels pronounced – are they long or short? or what if you have a word like filii, which is has a short i after the l, but a long i after that? Do you hold them out especially long, or what?

2

Best to think of them not as double vowels but simply as two successive vowels. Sometimes however they can coalesce, so that gen.sing. of filius may be just fili (-li with long I, of course) instead of filii (-lii short-long). They’re not difficult to pronounce.