Brothers battle it out for their senile dad’s inheritance while they encounter unforeseen changes in their DNA due to an alien entity.

I like the idea of combining sf and brother's battle. This is what is interesting for me and in my opinion you should keep it. BUT you have to build a strong link between the two concepts so that it will become One concept. The heritance and the sf element could be combined.

for exemple:

"When two brothers found a mysterious sphere at their senile father's house, they start battle over the inheritance while experiencing strange mutations in their bodies and minds".

I don't see the point of the alien DNA technology as a plot gimmick. Or the need.

If the purpose is to introduce a factor into the story that alienates two brothers who were previously simpatico, living in harmony, you don't need to tweak their DNA. Fighting over an substantial inheritance left intestate can divide and alienate family members who had been living in peace and harmony for decades. This I know from personal experience!

Also, by introducing the alien DNA tweaking, you seem to have rendered the characters as plot puppets of the alien; the alien is pulling their strings via their DNA. They appear to be victims who are not in charge of their own destiny. The conflict does not arise from their own character flaws. It arises from an external, an alien factor, over which they have no control.

I don't see the point of the alien DNA technology as a plot gimmick. Or the need.

If the purpose is to introduce a factor into the story that alienates two brothers who were previously simpatico, living in harmony, you don't need to tweak their DNA. Fighting over an substantial inheritance left intestate can divide and alienate family members who had been living in peace and harmony for decades. This I know from personal experience!

Also, by introducing the alien DNA tweaking, you seem to have rendered the characters as plot puppets of the alien; the alien is pulling their strings via their DNA. They appear to be victims who are not in charge of their own destiny. The conflict does not arise from their own character flaws. It arises from an external, an alien factor, over which they have no control.