Make case stronger

Hi. I need advise
I am a Bangladeshi national in the UK. The whole family came here on a diplomatic visa. Me and my brother were still studying when my dad's posting ended in April 2008. We stayed on to study and continued working. Come 2013, we realised we have overstayed and we are illegal! I knw... Stupid right! We genuinely didn't know we overstayed. Like I said, after we graduated we worked and paid tax. Our visa was accepted and we didn't knw.
So we decided to apply and this is our 3rd time applying for flrfb, based on article 8. Funds are running low and this is our last time.
I have have finally realised how incompetent our solicitor is. So I need help as to what needs to be added to make our case stronger.
Any advice is appreciated!