Back in the early 2000s a small band of UK-based Tongan international rugby players used to hold regular community gatherings to share improbably huge meals, pray and socialise together. Fe’ao Vunipola, Kuli Faletau and Keni Fisilau were all from the same club at home and, over the years, their respective wives and children effectively became one big extended family.

To say the national teams of England and Wales, along with the British & Irish Lions, have derived some benefit from this bulging houseful of expat Tongan muscle would be the most colossal of understatements. Between them Fe’ao’s sons Mako and Billy Vunipola earned 154 caps for England while Kuli’s boy, Taulupe Faletau, has played 104 times for Wales. Now it is time to meet the Fisilaus in the shape of Keni’s 20-year-old son Greg, the back-row who made his England A debut in February and will start on the bench for Exeter against Bath in the Champions Cup last-16 on Saturday.

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Given Greg’s relative inexperience, his rate of progress since arriving at Exeter from Wasps barely 17 months ago has been remarkable. “It’s incredible to think he’s still only 20,” says Rob Baxter, Chiefs’ director of rugby. “Physically he’s still just scratching the surface. He doesn’t look that big and then he gets on the scales and he’s 110kg.” With even more turbocharged Tongan power still to emerge in the view of Chiefs’ strength and conditioning staff.

That said, if you talk to Keni, his hard-working, personable eldest son could soon have some serious family competition. Anyone out walking in the Oxford area this week may already have spotted a 10-year-old doing hill sprints and the boy’s name is a further giveaway. “We call him ‘MB’ but his name is Makobilly,” reveals Keni, proudly. “We gave Mako and Billy’s mum the honour of naming our little one and she named him after her boys.” OK, so what’s the latest from the hill? “Yesterday, while I was away driving my middle son to Warwick, I told him to go and do 15 runs on his own. When I came back I asked how many he’d managed. He said 10.”

If you are starting to wonder if the 47-year-old Keni, once a hard-hitting centre for Plymouth Albion, is a fan of tough love, you would be right. In Greg’s case it began before he could walk – “When he started growing I just tried to make him crawl up and down the stairs” – though Keni ruefully concedes he nearly went too far at times. “When Greg was young he’d turn purple every time he went running but he’d never stop. He’d be crying but he’d still keep going. It was only later that I found out he had asthma. I thought: ‘Oh no, I nearly killed him.’”

Legend also has it that Keni initially declined to take the Plymouth-born Greg to tag rugby because of the absence of contact, though the truth is more nuanced. “On Sundays we were going to church so I didn’t take him to mini-rugby.” Nature eventually took its course, however, and Greg started playing at Devonport Services and, subsequently, Oxford Harlequins when his father became player-coach there. “We are Tongan,” says Keni. “Rugby is in our blood from home. I have two older daughters but I just kept praying for a son. And then he arrived!”

The Fisilau siblings have always been encouraged to make their mark in some capacity. The eldest sibling, Lisia, is in the RAF and her sister, Malieta, has a degree in business and law. A teenage brother, David, is in the RFU’s Midlands academy and then there is Makobilly, who has recently been offered a scholarship to a leading local preparatory school.

It is quite the success story given the visa problems that almost forced Keni to depart the UK before Graham Dawe, his erstwhile coach at Plymouth Albion, intervened on his behalf. In return Keni and his wife Camilla granted the former Bath and England hooker the honour of choosing their first son’s name. Fast forward 20 years and Greg’s respect for his parents is similarly deep-rooted. “Dad’s a very hard man. He did a really good job of teaching all of us to stay humble and to work as hard as we can. He and mum pushed us all from a young age to try and reach the potential we couldn’t see at the time. I’m glad they did. When you get older and look back you understand why. I’m grateful to have parents like that.”

The next collective goal is for Greg to press on to a full England cap – “It’s always in the back of everyone’s mind to be able to represent their country at the highest level” – or at least to go on tour to Japan and New Zealand this summer. Fisilau Jr has not always been a nutritionist’s dream – “I used to be on the old ‘seafood’ diet: see food and eat it,” he says – but his deceptively strong ball-carrying and work-rate are now his calling cards.

He has certainly rebounded splendidly from the shock – “I’d almost go as far as to say it was pretty traumatic” – of his first professional club Wasps going belly up, followed by a daunting Premiership debut for Exeter against a fully-loaded Saracens team featuring both senior Vunipolas. “I wasn’t supposed to be playing but got thrown in a couple of days before. I remember standing there, waiting for them to kick off, and I was physically shaking.”

There were few apparent nerves, however, when he and Exeter stood firm against Toulon’s pack in an intense Champions Cup pool game in December and there will be none off the bench this windy weekend against his one-time Wasps colleague Alfie Barbeary, now a Bath totem. Baxter compares Fisilau’s ability to make an impact on games with England’s Immanuel Feyi-Waboso and suggests the former’s value is most obvious when he is not in the squad. “When he was missing this season it was so noticeable not having him in the team. That’s the biggest compliment I can give him.”

As it happens Fisilau, currently living in the hotel next to Sandy Park, and Feyi-Waboso are set to be flatmates next season and they play basketball together in their spare time. If the former ever requires top-level back-row advice, though, the family know who to call. “I saw Billy over Easter and he said if we had any questions just to give him a shout,” says Keni. “The Vunipolas and Faletau have known Greg since he was a baby and he’s grown up looking up to them. They opened the door for young Tongans in England.” If, as Greg suspects, Makobilly also joins the family trade – “Dad reckons he’ll be the best out of all of us” – there could soon be another on the horizon.