All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is unlawful for a woman to travel in long trip except with a Mahram (non-marriageable man). The husband of her sister is not Mahram even if he is accompanied by his wife. The evidence for this is the following Hadeeth.
The Prophet said: “The woman should not travel for three days except with a Mahram.” All this in order to preserve the dignity and rights of the woman.
As for your other question, Abu Hurayrah narrated that the Prophet said: “Allah created Adam in His Image, sixty cubits in height. When He created him, He said (to him), ‘Go and greet that group of angels sitting there, and listen what they will say in reply to you, for that will be your greeting and the greeting of your offspring.’ Adam (went and) said, ‘As-Salaamu alaykum (Peace be upon you).’ They replied, ‘As-Salaamu-‘Alaika wa Rahmatullah (Peace and Allah’s Mercy be on you).’ So they added ‘Wa Rahmatullah.’” The Prophet added, “So whoever will enter Paradise, will be of the shape and picture of Adam. Since then the creation of Adam's (offspring) (i.e. stature of human beings is being diminished continuously) to the present time.”
Dhiraa' is what is between the elbow and the tips of the fingers.
Allah knows best.