Fasting on only the 10th of Muharram due to some valid excuse

Q: I have read that it is makrooh tanzihi for one to fast on only the 10th of Muharram (without also fasting on the 9th or 11th). My questions are:

1. What is the ruling if one could only fast on the 10th due to some valid reason?

2. Should he rather not fast on the 10th?

3. What constitutes a valid reason?

4. What's the meaning and ruling of makrooh tanzihi?

Paying back a loan to the heirs of the deceased after the death of the creditor

Q: I borrowed 40000 US dollars from a friend of mine in America in 2008, which was equal to Rs 2500000 at that time. Our verbal agreement was to return the money in dollars. I could return $33000 through money changer, then there was a ban to transfer of dollars to another country. My friend passed away in America. I informed his family about the remaining amount and requested to collect that through someone travelling to Pakistan. After that there was no answer. I sent a registered letter on the given address but that letter returned to me as there was nobody to receive it. There had been correspondence on that address. I tried to trace them by other means but could not find them. Three years have passed. The Dollar rate has increased more than double. Please advise me in this regard.

Marrying a married women

Q: I married a girl and she was already married to a guy. For the last 4 years he was in a jail due to some reasons... The family members doesnt have any information about their son. And his wife also dont have any information about her husband whether he is coming out or not. There was no information at all regarding her husband so we had done nikaah. Is it right or wrong? Is she still married to her first husband? Her husband was calling from jail and he was not saying whether he was coming out or not. Now after 4 years he came back to India. What must do?