Ok - so a couple things......
this is mostly with #3, but I have known 2 sets of families who named their 3rd son Trey (the 1st spelled Trey and the 2nd Tres, with the accent).... which means 3rd.
Also, Bill Gates III went by Trey as a kid.
Dewi is the Welsh form of David..... but is also pronounced like Due (or 2nd). Some families have used that as an option.
I also googled and I guess it's not UN-common to just name your son Junior. As in, his ACTUAL name is Junior.
You can do whatever you want.... but if you don't do it right, you will hear about it for the rest of your life. So, as mama's said below...... Your son would have to be Todd Michael Ross, Jr.
Now.... plenty of people get this wrong. which is why many refer to George Bush, Jr and George Bush, Sr. TECHNICALLY that is incorrect.
George Herbert Walker Bush
George Walker Bush
Even though the names have 2 out of 3, it's still technically incorrect to refer to Baby Bush as the Jr of Daddy Bush.