If they do the act of penetration in front of two witnesses they get the death penalty if fair warning is given by two witnesses. That means this: the witnesses have to tell them the act they are doing is forbidden, and that if they do it they will get the death penalty. [If they admit it then you don't need witnesses.]
Besides that there is a kind of spiritual penalty called Karet כרת being cut off from ones people involved. And that applies to all the types of forbidden sexual relationships that are called עריות incest. Incest is actually only an approximate translation because it also refers to sex with a woman who has seen blood within seven days of her seeing blood. Also one can't have sex with her unless she has gone to a natural body of water (note 1) like a river or sea and dipped in completely from head to toe.
Actually, stoning is not the penalty for homosexuals. I think is is burning. But I am not sure. I would have to look it up. That means you take lead [It does not have a high boiling point] and heat it up until it flows and then you pour it down their throats.
Appendix: If the two male homo-sexuals think the act is allowed, that counts as being accidental and they can bring a sin offering. [I mean to say that an accident can be either thinking something is permissible or in making a mistake about material facts.] That means they have to bring either a sheep or goat to the Temple in Jerusalem and have the priests sacrifice it as a sin offering. They can't eat any of it as a barbecue. The part of the animals that are not burned are eaten by the priests. This is always the rule for sin offerings. If you want a barbecue in Jerusalem together with the mitzvah of bringing a sacrifice, you have to bring a peace offering or a thanksgiving offering.
Mishna Zevachim chapter 5.
Rambam Laws of Sin Offerings. [That is located in the book on General Sacrifices.]
Tractate Macot concerning fair warning that must be given.
I should mention that there is no prohibition to bake cakes for homosexuals. On the contrary, it is a mitzvah to be nice to them and to tell them that what they are doing is terrible, horrific sin.
Now this seems to be a subject of a debate. Sometimes it seems like you are supposed to tell people that they are sinning even if you know they won't listen. And sometimes it seems not. I really can't tell. My own approach to this varies according to the situation.
(note 1) If no natural body of water is available, she can make her own mikvah. The mikvah has to be attached to the ground, and cannot be a vessel. And it can't be such that if lifted that it stays intact.
There has to be about 1^3 meters of water. [This amount I forget. I would have to look it up. I think it is about 1^1^1.33 meters.]
(note 2) If there is no Temple, they are still legally required to bring a sacrifice. They would have to build the Temple according to the proper specification in the Mishna Tractate Midot and hire a few priests and find red hefer. They can do it but it would be expensive. Besides all of that there is some doubt about the proper location of the Temple. Some archeologist have apparently discovered the remains of the First Temple in the area when you leave the Western Wall to go back to the New City you pass on the left. This whole project is so hard that it makes more sense not to sin in the first place.