From looking at their previous posts, ajayre's wife has just applied for citizenship, so they would both be UK citizens.
In which case, using the NHS will have nothing to do with visa status and everything to do with maintaining ordinary residence in the UK.
As UK citizens, if they have lived outside the UK for more than 3 months in the previous year, they are not entitled to free NHS care UNLESS they have been working abroad for less than 5 years AND have lived in the UK continuously for 10 years at some point.
So, assuming
ajayre was born and raised in the UK, he would still be entitled to free NHS care during the 6 months in the UK , however his wife would not, as she has not lived in the UK continuously for 10 years.
From the NHS:
Entitlement to Free NHS Hospital Treatment by Non-Resident UK Citizens
This leaflet has been compiled to explain the entitlement requirements for free NHS hospital treatment in the UK for Non-Resident UK Citizens.
• The NHS does not normally provide free hospital treatment for people who do not reside in the UK even if they are UK nationals
• If you have lived outside the UK for more than 3 months (6 months for some pensioners) in the last year you can be charged
• You will be exempt from charges if you can produce evidence that you have been working abroad for less than 5 years and have lived in the UK continuously for at least 10 years at some point
• If you are residing in another European Economic Area member state you should show your European Health Insurance Card from that country or apply for a Provisional Replacement Certificate where possible
• If you have come to the UK from a non-EEA country that the UK has no bilateral agreement with you will be expected to pay for treatment unless another exemption applies to you