“Is there a way to have two people of the same sex have a kid who is biologically related to both? (Either gay or lesbian couples)”
Short answer: Yes! But it’s complicated.
Long-ish answer: Creating a child from same-sex parents isn’t as easy as just combining the DNA from two eggs or two sperm. The main problem is genetic imprinting, where gene expression is modified epigenetically. That just means the actual sequence isn’t changed, but something else is edited, like adding methyl groups or modifying histones (the proteins that help wind up DNA).
And depending on if you’re a mother or a father, you genetically imprint your gametes differently. And since you generally need one functioning copy of these select genes, it doesn’t help to have two female or two male versions where they’re both turned on or off (too much or too little can both be harmful).
While that seems impossible to overcome, science is pretty impressive. Researchers have already overcome this in mice, where two egg cells were used to produce fatherless mice. So yes, it has been done in another animal!
However, who knows when or if we’ll ever see it in humans. There are always ethical concerns when you’re dealing with human subjects, and it’s hard to predict if offspring would be completely healthy using this method. I think you’d have a hard time getting this past a review board since it’s not a necessary medical procedure – same-sex couples don’t need biologically related children, even if it would be nice. But, you never know.