There is a risk of inbreeding https://twitter.com/GaneshaRavindra/status/1199005714779267072

For starters your family tree would look like this

This is the first generation, i.e. your grandparents

Note : blue is your grandfather's genes

Red is your grandmother's

This is the second generation representing your Bua and fufa

Note : Purple represents fufa's genes.

This is the possible cases for the third generation i.e. your bua's daughter and you.

Note: orange represents your mother's genes

See that there is a 50% chance of subject and bua's daughter to have the same gene inherited through the grandfather

Taking the case in which bua's daughter has grandfather's genes, there is a 25% chance of having an offspring that has mostly your grandfather's genes. A case of inbreeding! Although the X and Y chromosomes don't pair up so there are no chances of 2 recessive genes being +

+ homozygous, the risk is less but still there are normal chromosomes too.

Also look at the second case in this punnet square. The offspring has genes from your father's wife and bua's husband