Just need a basic guideline if possible! (Can go to an Assesoria if we need to take things further…)

OH is retired, gets UK pension.
But has recently started doing gardening again and wants to sell on any surplus (probably around Eu500 pcm as it has now become their raison detre!)...

We have been strongly warned that the ‘Inspectors are out’ and fines are being given where anyone who does the above (and it is not proven that it is only for family use), has to register as autonomo.
No worries, as we submit a tax return each year anyway.

However, the cost of autonomo as many of you know is very high (Eu250+?) 
We have been told that as an agricultural worker they might only have to pay Eu150pcm Social Security (and of course any annual tax on combined incomes.)
Can anyone confirm this?

We want to do things right, but need to know we are doing the right thing (if you know what I mean - as we are on a very tiny budget in the first place.)

1 person to our knowledge has been ‘inspected’ already (they were just about able to prove the produce was for family/extended family.) But as we are 2, we know we cannot do this.

The other alternative - is to not do the market garden. However, we do need to top up the income, so are going to have to make a decision one way or other regarding leagalizing things sooner than later.

Further thoughts:

What is the annual allowance for a single 64 yr old? (we are not married or officially co-habiting.)

Are there any tax breaks for 64 year old? or is it the 65 years threshold as per a Spanish National?
Would there be any further SS or Tax breaks when OH reaches 65?

Any information welcome! 

(PS - our combined income is very low. I am unable to work due to disability, but get no allowances etc.)