Both players are back row forwards. Ollet, 21, has made 10 first-team appearances since his debut last year.
Holiker, 18, is yet to play for the first team, but has had a campaign disrupted by injuries. He hopes to put that behind him, and establish a place in the first team soon.
“It’s been a pretty tough season with injuries but I didn’t want to go anywhere else and I couldn’t be happier to sign up for another couple of years,” he said.
“I’ve now got a chance to build my fitness up over the next few weeks in time for the business end of the year and then the focus will be on having a strong pre-season.
“I’d love to join the likes of Aaron in getting a first team debut under my belt and Chezzy (Chris Chester) has shown he’s not afraid to throw the young kids in.
“That gives me a lot of confidence that I can come through and make a name for myself, but to train with and learn from players of the calibre of Mick Weyman and Neville Costigan is also great for my development.”
Ollett, meanwhile, is relieved to have his future resolved, and is targeting more first-team appearances.
“It’s a weight off my shoulders to sign a new deal and now I want to kick on and have another strong season next year,” he said.
“I’ve been pleased with the amount of games I’ve had at the back end of this season and I feel as though I’ve been able to prove my worth to the club.
“It always helps to have a consistent run in the team and having a few games on the bounce in the past couple of months has definitely made me a better player.
“It’s now up to me to cement a regular first team spot next season.”