Under 18's single vaccination rules and travel

jow4396

We are flying to Tenerife on 20 October and my twins, aged 16 have both had a single vaccine.  They are having their 2nd on the 19th October, but due to the 8 week rule, I can't get it any earlier.  According to the Spanish rules, vaccines have to have been given 14 days prior to travel to be counted, so I am currently classing the twins as only having one vaccine.  However, in general most children are only being offered one dose, so how does this affect things with regard to testing?  In addition, they both had Covid in July and we were told by NHS they shouldn't have a PCR within 90 days or it can show a false positive! I can't find anything about it on the government websites etc.  Any help or advice would be much appreciated thank you