The duo have both established themselves at Vicarage Road after moving in the summer, with Femenia coming in on a free transfer from Alaves, while Richarlison joined from Fluminense for £11.2m.
And while the defender believes he is developing at the club, he believes Richarlison would benefit from extending his stay at the club.
"I think he is still a very young player, he shows great potential, he did very well this year and he has helped us to win games. But, of course, he is young and I hope he stays here. We will help him to get even better day-by-day," Femenia told Goal, before talking about his own future.
"Of course, if I could I would stay for my whole career. I think that there is a difference between La Liga and here and it is better here for my style of play. I would like to stay here. Watford was the team that bet the most for me.
"I thought the most difficult thing was going to be to relate to the different kind of people here in the UK. It was easier than I thought, I managed to get used to it in a quick way. I speak with the people who talk my language in the dressing room.
"So mainly Perreira, Britos and Carrillo. They have been very helpful, especially in the beginning, they have been my point in the middle and they are my team-mates.
"I think what has surprised me the most here in the Premier League and the big difference with Spanish football is that nothing is finished until the 90th minute, or whenever the referee blows his whistle. I have seen games where we are winning 1-0 and we end up losing 2-1 in the last minutes.
"No one gives up when losing, maybe in Spain when you are losing one game and it is only five minutes left, you know it is going to end like this. It is very difficult to change it. Here, you can win, draw or even lose the game in those last minutes.
"I used to see all these stadiums when I was watching on TV as a kid. Now I have got the opportunity to play in them and what has surprised me a lot was the Emirates at Arsenal, it is a great stadium. I think that any football player would like to play in these stadiums.
"My dream is to play here in the Premier League for as many years as possible and to stay here. If I have to go then I will go but I want to play here as much as possible."
Watford could secure their highest ever Premier League finish with a win over Manchester United on Sunday.