You can drive up to 7.5t lorry if you passed test pre 1997 so no issues there.
The landy is likely to be able to pull a trailer with one horse
or two ponies in it
or some goats/pigs. For eg an Ifor Williams 510 horse trailer weighs about 900kg-1000kg empty, so add the animals weights and then check against your Landrover model via Google or any of the towing forums online. My Landy can do 3500kg but it is a long wheelbase 110, so it might be less for short wheel base 90s
You actually only need a competence certificate if you are transporting the animals as part of an economic activity (ie business). The 65km (30 mile odd limit) also applies only to businesses, for them over this distance and under 8 hour journey a Short Journey Transporter licence would be needed, with a Long Journey Transporter licence needed for journeys over 8 hours.
Of course, in the event of a check it would be for you to prove that it was not a business, so any aspect at all of money changing hands would make it worthwhile to get a competence certificate and (if needed) licencing. And of course with or without any certs, everyone is obliged to know and follow the guidelines for assuring livestock welfare in transit.
Link here to the relevant info
https://www.gov.uk/farm-animal-welfare-during-transportationYou will always need to do full movement documentation for any livestock (not including horses, tho their passport must travel with them), except for certain limited pre agreed exceptions.
There are also standstills triggered by movements to consider (tho breeding rams are excluded), as are movements direct to slaughter.
It is a lot simpler to ship a couple of ponies around with their passports than the livestock, paperwork wise! (NB nominal prize money at a show or petrol contributions have been adjudged not to count as making you a business)