According to the linked article, heterosexual couples do the adoption route (so that both mum and dad have legal parental responsibility, not just dad)
This is not a route open to gay couples due to Kenya’s legal position on homosexuality so bio dad has to have a DNA test and then go to court for a parenting order that relinquishes the birth mums rights.
The court can refuse to sign off on adoptions and parenting orders. Nothing is guaranteed due to Kenya having no specific surrogacy laws, just a hodgepodge of other laws that are being adapted or loopholed
Both court processes are long and expensive.
It’s all in the linked article. Bio dad can’t just pretend to have conceived with surrogate mum in a normal way and take the baby because they don’t let Kenyan born babies leave with foreign, non resident dads who aren’t married to mum under Kenya’s prevention of trafficking laws (presumably they have a good reason to organise things this way? An unmarried foreign dad without legal parental responsibility wouldn’t be allowed to leave the UK with a newborn either, especially when the baby doesn’t have a passport).
Besides, all the hospital staff are well aware that mum was a surrogate, so dad can’t start denying it now, that would be fraudulent. And acting fraudulently would be sufficient reason to take the babies into social services care.
And yes, the babies will be entitled to Irish citizenship but dad can’t apply for Irish passports until the DNA test and birth certificate paperwork is complete. This all costs money.