Re: Sempai-Kohai relationship
I think it is sort of a moot point whether a 6th Kyu person is sr. to another 6th Kyu person because you both know very little in the scheme of things. Are you not allowed to train with other people or it is your preference to work with these people? I think it advisable to train with people who outrank you if possible. Generally, the highest ranking person should be your goal. Hours of training is important but also the quality of your learning experience. That will also avoid the question of who is sr. to whom.
What I'm used to is the person who outranks you is sr. and therefore you always attack them first. That may vary in your dojo to hours of training being first but whatever is used to determine senority. The jr. person may know more about the particular technique, etc... but the jr. person always attacks first and gives instruction if asked. The Sensei is expected to come around to the various pairs and to give advice as needed.
If you can focus on your own training, that is best because it is so easy to get caught up in trying to teach one's partner and who knows more about what rather than learning for oneself.