The half-backs are out of contract at the Liberty Stadium in the summer and have been targeted by big-spending French clubs.
But Ospreys head coach Steve Tandy remains hopeful of retaining the pair's services.
"Without any shadow of doubt we need the likes of Kahn and Biggs to help build the group we have," said Tandy.
"We're hopeful of keeping both of them.
"Kahn's world class and great to have around on the training field because his influence rubs off on the younger players.
"Not only is he a great ball player, he also understands what we want from a game, runs it well and is huge defensively."
Fly-half Biggar indicated his desire to stay in Swansea over the weekend and revealed he is close to penning a new contract.
Northampton Saints are the latest club to be linked to Fotuali'i but the Samoa scrum-half has joined Biggar in declaring he would prefer to stay put.
"It's something we need to talk about further on, but I'd be very pleased to stay, " said Fotuali'i.
"We have a great bunch of boys here and the future excites me a lot.
"My focus in on helping out on and off the field.
"We're out of Europe but there are positives to come out of the campaign.
"We have a great bunch of boys, some quality youngsters coming through, and it's testament to what Steve Tandy and the other coaches are doing. Everyone is buying into what the coaches are doing. Everyone is getting on board."