Interesting questions...
Human, Fur or another kind?
Human - two grown men, although somewhere back there they were babies, then boys... Live close but independent from us.
Fur - One crazy cat. Two before Monday, but we had to have our beloved Lucy put down. She was over 15 ( old lady for a cat) - he is younger, but not by that much. I think I may be looking forward to the empty pet nest soon.
I also have two grand dogs, three grand cats and maybe a grand child on the way... Order of birth, not favouritism implied.
Age differences between them?
my sons are 4 yrs apart. Come to think of it so were my cats. My first son decided to only sleep about ten minutes in every hour around the clock after he was born, and I swore I would not have another child before he slept through the night. Took almost three point five years.
Personality differences?
Yes. Where Alex never slept, Jason came along and slept 11 hrs straight from week one. We prayed Alex would sleep and we watched over Jason praying he was ok because he slept so much...
They are still totally different. Alex is darker with the lovely creamy Greek olive skin. He is analytical and precise, serious to a fault, competitive, driven. Everything must be perfect. He is impatient but extremely sensitive and kind. He is the proud Aries, he is also the Horse in Chinese astrology, a proud hard worker, compliment to my own fierce silver tiger. His size and shape take after my husband, five eleven, low center of gravity like a football defensive line. He is extremely athletic and physically strong. However, even though he has my husbands family's physical characteristics, he wears my face. He is charming and handsome in a dark rugged hockey player way. I love my sons equally, but in spirit, ideology, and shared confidences, Alex is most like me and we are very close friends.
Jason is the artist. Flights of fancy. The boy wonder who will reinvent the universe. He is an Aquarius. He is so alike in build and looks to my father, sometimes it is scary. My children, who barely knew my parents, have convinced me of genetic memory. If you watch Jason walk or talk - he is his grandfather. He has my family's complection of Northern Europe, fair and freckled. Tall, he is 6 ft 5 inches. He is a natural salesman, charming to a fault, gifted in music and art, more ethereal and imaginative than his brother. He inherited the engineering gene from my husband's side. The men in that family can take apart anything, fix it and put it back together better than ever. Jason does this with an imaginative creativity.
He confides in me, but his comfort zone is in sharing stuff is with his father in their shared business and opinions in life.
Do they get along?
Yes and no. Sometimes. Mostly. They have different personalities and different directions in life. They share many friends acquired growing up, yet they have many friends each, that the other doesn't get along with. I always opened my door and heart to any and all of their friends, assuming it was better to know who they were with and what they were doing. They had and have the same great friends since they were so small. It's given me the privilege of watching many of their friends grow up and still have them at my dinner table for holiday celebrations, alone or with wives and children... as men. It's a blessing and a strange curse. if there is sadness or strife as they navigate life, I worry and wish I could fix, but understand I cannot always change things.
The one thing I can say is that we are a very close devoted family in the ways that I think truly count. We may disagree and yell and claim we won't speak to each other ever again, but, if one brother is in trouble, the other will move heaven and earth to make things right. If one brother needs help, emotionally, financially, whatever the other will step into the breach and do whatever possible to mend.
We fight, we argue, we disagree with that Greek passion I have learned to admire, but we are always ready and willing to step into the fire for each other.
How did you pick their names?
Finally an easy question, and, sort of, strange family history.. I was told when I planed my wedding (after I was baptized into the Greek Orthodox Church) that a first born son is always named after the father's father, if a girl, after the father's or mother's mother... Hence, first son is Alexandros.
Most female converts are baptized into the Greek Orthodox Church as Maria after the Virgin, but I chose my fathers's mother's name of Helen as I was the first girl in my family and it was appropriate to pick the name of my father's mother. This was before I knew anything of my future children or how I had to name them. Elenie or Helen is my legal name although I don't use it except with my Greek family.
Remember, Helen of Troy, and Helen the mother of Alexander the Great. Alexander was my husbands father's name so Alex for my first born seemed not only auspicious, but an easy choice.
Second born if girl would have been Laura for my mother, or Katherine for his mother and/or (strangely my sister who bears this name only because my own parents let me name her)..
No girl in site for five generations in my husbands family, so 2 was a boy and should have been named for my father, but the Welsh name (Nevin) did not sound so good with Zenebisis, so we went back to Ancient Greece. His name on his birth certificate is Iason, pronounced E'yason, as in the story of Iason and the Goldn Fleece, most of you know as Jason and the Golden Fleece. We call him J. And his name and the quest he seems to have chosen in life fit the ancient history.
Sorry to be so long winded, but you asked...
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Sugar is just now (after 1.5 years) starting to accept the kids playing with her... sometimes. Other times she just goes outside or down the hall to hide. 
I also have one granddaughter and a grandson on the way 
my daughter's name was just a sweet classic english name ... i thought it was old school but turned out to be the most popular name for her birth year. (ugh)