Sebastian told MailOnline Travel: "We took a few weeks to get them used to it and set up the tent in our old front room - they genuinely loved it.
"By the time we had sold everything to fund the trip they were comfortable in the trolley and tent, they were and still are inseparable."
In a bid to explore the country beyond their home in Barcelona, the plucky quartet started visiting a number of Spanish national parks, including Sierra Nevada, Sierra de las Nieves, Parc Natural del Garraf and Montserrat.
One-year-old Luigi the cat and Bandito the pug, seven, have not only tackled some of the most beautiful Spanish spots, but have also racked up tens of thousands of Instagram fans in the process.
Uploaded images show the pug and feline riding on backpacks or happily trotting through picturesque scenery.
And like any brothers, they enjoy playing games with each other to keep entertained during the journey.
Sebastian said: "They love each other and are constantly bugging one another and playing tricks."
Sebastian and Finn ensure the cheeky pets have regular breaks so they can explore the surroundings little by little and learn the rhythm of the walking pace.
Sebastian said: "The trolley or tent are 'safe' areas so they always return if something has spooked them - mostly Luigi in the beginning and Bandito after he felt he had walked enough - he loves sitting and observing being pushed along.
"We knew we would turn back if it became stressful or unfair on them, they are the main priority all the way - as well as walking about 20km a day of course."
After spending the day in the fresh air, the four get some well deserved shut-eye in their tent.
The couple have plenty of advice for pet owners considering taking their furry friends with them on holiday.
"It is easy if you act like it is their holiday but not if you overestimate your pet's abilities," Sebastian said.
"We have had to be vigilant at all times. Inner cities are not ideal places, but fortunately we are in the countryside the vast majority [of time]. Because of this we can really enjoy our time together like climbing trees with the cat and running around with the pug."
And the travellers, who now live in the hills behind Marbella, have no plans to slow down.
"We live in an amazing area of mountains and forests, although it's hard to go in the summer with the heat. We take the boys out in the trolley because we don't want them to lose the trust they have in it.
"We are four very happy boys at the moment and Finn and I are very grateful to Bandito and Luigi for this journey."
