I am doing biological research and having some questions.

I have 4 different groups of transgenic mice (A-D) and want to compare tumor sizes each other (group by group).

A=control (wild type), n=3 mice
B=gene B overexpressed, n=4 mice
C=gene C deleted, n=4 mice
D=gene B overexpressed & gene C deleted, n=3 mice

Hypothesis of this study is that overexpression of gene B or deletion of gene C may induce tumor (by increasing tissue weight), and both may synergistically induce tumorigenisis.

I sacrificed them, took tissues and measured their weights.

For example, their weights are as followed,
(unit=gram)

A= 0.3/0.4/0.5
B= 0.6/0.7/0.8/0.6
C=0/7/0.8/0.7/0.6
D=1.1/1.2/1.2

First I want to calculate average/mean (dont know what is correct term in this case).

Second I want to compare them group by group by calculating p values to see whether the difference is significant (our hyp is correct or not).
group A vs B
group A vs C
group B vs D
group C vs D
In short, I want to see if B/C is heavier than A and D is heavier than B/C. (I will say their differences are significant/our hyp is correct if p<0.05)

Now questions are followed.

1. Do I have to calculate average or mean?
2. What Test do I have to use to get p values?
3. When I draw the data above in Excel Bar graph, I want to present average/mean as well as 'deviate'. What deviate do I have to use? Standard error(SE) OR standard deviation(SD)?

Thank you su much in advance!

Thank you so much in advance!