its an excellent exercise.
it boosts my confidence

That's great Tawheed. Hope you'll always find these useful. Keep it up!

thanks for acknowledging remarks.
this goes a long way in learning.
it shows there is someone who can help us learn in the hour of need
JAZAKUMULLAH KHAIRAN

1st question: In regard to the final greeting formula in your grand dad's letter
حبيب إلى حبيب
what would the formula be if I (male) wrote to my girlfriend, or if a female person wrote to either a male, or a female person?

2nd question: I think to have seen that the transcriptions of a word seems to vary between lessons at times. As far as this concerns the short vowels, it is not really important. But the dupplication of consonants should always stay the same, even in a different context, at least at my present level of knowledge?

I am a beginner, but all your lessons are great.

If you talk to your girlfriend or wife, then you can use almost the same sentence (من حبيب الى حبيبة), hope you can spot the slight difference. The same happens if she is writing to you, she just switches the words (من حبيبة الى حبيب). Things change if the relationship is different, like teacher or colleague at work, but general speaking, it is fine for females to address each other as (حبيبة) and same for males to address each other as (حبيب), it is very normal in the culture for a female to call another (حبيبتي - my love) or a male calls another (حبيبي) it is just like saying (my dear) in western culture.

To answer your second question, short vowels are important when you speak, in fact they might make major change in the meaning in some cases. In writing, they are less important as people know them from the context. You'll notice that we don't apply the 7arakaat in the transcript to reflect the reality of the street, if you get a newspaper you'll not see those 7arakaat, so best thing is to get used to the sound and you'll find it straightforward once you are used to it.

Hope that answers your questions.

The nearest English equivalent to حبيب is probably 'dear' 'm'dear' (my dear) which used to be quite commonly used for either sex in northern England but has largely fallen out of use over the last few decades although it can still be heard, as can the Midlands equivalent 'mi duck'.