"Tie-breaker" rules for IUPAC nomenclature of organic compounds
For Question 1

Example 1


You should select the (green + blue) chain because, no matter which among the blue and yellow you pick, the numbering would not start from the green chain rather the yellow or blue.
Now if you pick the blue chain the substituent ($\ce{methyl}$) would get number 4, whereas if you picked the green chain the substituent($\ce{isopropyl\ or\ methylethyl}$) would get the number 5, so in accordance to the First Point of Difference Rule you should select the green + blue chain.
Also Worth noticing is the fact that no matter which chain you pick, the other chain which becomes the substituent would always get the number 7 

So locants (4,7) are better than (5,7).
$$\begin{matrix}
\text{Better name:}&amp; \text{7-(2-isopropylhexyl)-4-methylheptadecane}&amp;\\
\text{Rather than:}&amp; \text{5-isopropyl-7-(3-methylhexyl)heptadecane}&amp;
\end{matrix}$$



Example 2

  

In this case according to the above mentioned rule, you should check the position of the double bond, now since there is a double bond already in the green chain at the first position it would get number 1 and the numbering would start from there.
If you choose the green + blue chain the other double bond would get number 5 and for the green + yellow chain the other double bond would get number 6. So you should go for the green + blue chain in this case.  

So locants (1,5) are better than (1,6) with reference to double bonds.
$$\begin{matrix}
\text{Better name:}&amp; \text{(5}\textit{Z}\text{)-5-ethenylhepta-1,5-diene}\\
\text{Rather than:}&amp; \text{(3}\textit{Z}\text{)-3-ethylidenehepta-1,6-diene}
\end{matrix}$$



For Question 2

If the chain has to be numbered and two substituents have the same locant the n you see the alphabetical order of the names of the groups/substituents and if they are also the same it only means that they are the same substituent and hence are written together with there locants separated by a (comma),.  

For example in you would name the below compound as 
$\text{2,4-dichloropentane}$




For Question 3

Example 1


The substituent in this example would be named $\ce{ethylidene}$. 
$$
\begin{matrix}
\text{Final name:}&amp; \text{5-ethylidenenona-1,8-diene}
\end{matrix}
$$
Similar substituents can be named as

$$
\begin{array}{|c|c|c|c|}
\hline
\ce{Substituent&amp; Saturated\ form&amp; Name\ of&amp; Name\ of \\
&amp;&amp; saturated\ form&amp; substituent \\
\hline
R=CH2&amp; R-CH3&amp; Methyl&amp; Methylidene\\
\hline
R=CH-CH3&amp; R-CH2-CH3&amp; Ethyl&amp; Ethylidene\\
\hline
R-CH=CH2&amp; R-CH2-CH3&amp; Ethyl&amp; Ethenyl\\
\hline
R=CH-CH2-CH3&amp; R-CH2-CH2-CH3&amp; Propyl&amp; Propylidene\\}
\hline
\begin{align}
\ce{R=C&amp;-CH3\\
|&amp; \\
C&amp;H3}
\end{align}&amp;   
\begin{array}{rl}
\ce{R-C&amp;-CH3\\
|\ &amp;\\
C&amp;H3}
\end{array}&amp; 
\ce{Isopropyl&amp; Isopropylidene}\\
\hline
\end{array}$$