Just replying to the above as I think I've figured an approach out.
"Roll up" each cashflow (including initial investment) to figure out the "V_T" valuation (this is what I couldn't work out initially):
e.g. for Fund A: 1000*1.15*1.1*0.85 + 150*1.15^0.5*1.1*0.85 + 400*1.1^0.5*0.85 + 100*0.85^0.5 = 1674.44
MWRR: 1000*(1+i)^3 + 150*(1+i)^2.5 + 400*(1+i)^1.5 + 100*(1+i)^0.5 = 1674.44. Same for Fund B.
