Is a little confusing the way you set it up. Maybe try a table next time?
I got Family B being the oldest family by ~471.9 years.
Family A math:
x+(X+4)+(x+8)+(x+12)
y+(y+2)+(y+4)+(y+6)+(y+8)+(y+10)
2+5+8+11+14+17+20+23+26+29+32+35
x+12 = (1/2)(y+10)
y=35
1/2(35+10)=22.5
x=22.5+46=68.5
68.5+73+77+81= 300
35+37+39+41+43+45 = 240
2+5+8+11+14+17+20+23+26+29+32+35 = 222
Family A total: 762
Not going to give my answer but plugin from there...
Family B math:
174/2 = 87
87/2=43.5
43.5*grandparents =
87*0.33333333=28.9999999
28.99999*grandkids =
0.8*28.9 = 14.499= 14.5
14.5*children =
12 *5 = 60
Add them together and get your age.
I don't want to show my full work/answers because I encourage others to think for themselves. @Nerdig and I disagree on the answers but this could even be due to a rounding issue somewhere.
I had a similar approach.
I spotted one mistake you did: 8+3 isn't 12.
Its quite possible that I made mistakes too.
Good catch. I noticed it in my notes but not on what I posted on here.
I got around 130 years more than you for Family B.