If my husband adopted my daughter would he get a VISA?

Doubtful. First, step-adoption is difficult. The court will look after the best interest of the child. It's what is the advantage for the child not the step-parent. Your husband being in the country on a student visa is sure to raise flags in this respect. Second, the only visa for parents of a British child are for when that parent has sole responsibility for the child or the child normally lives with that parent (him) and not their other parent (you) OR if the parent or carer that the child normally lives with is a British citizen or settled in the UK (you) but is not that parent's partner (which he is).

This is because a partner is expected to be in the country on a spouse visa.

He really needs to apply for a spouse visa which means you must meet the financial requirements.

Your case is particularly complicated so you should probably contact an immigration attorney.

Committing procreation is never grounds for any visa or immigration. Children derive rights from their parents. Parents never derive any rights through their child. Thus your 3 y.o. has a right to citizenship in her father's country of citizenship. He can get her a passport from his country & she can go & remain there forever as a citizen of that country. That father, of course, remains an illegal alien.

The one due in August will have a birthright to citizenship in Bangladesh as the child of a Bangladesh citizen. The Bangladesh father derives no rights from that child.

Having the Bangladeshi adopt the 3 y.o. is going to be a nightmare. The father must first relinquish all rights to his child. Plan on this taking a few years, if it can be done at all ever.

Neither child - even if he could adopt the 3 y.o. - is going to do anything for your Bangladeshi. ALL that happens is your 3 y.o. ends up with the right to citizenship in Bangladesh.

Hubby is going back to Bangladesh. He will have to apply for your immigration to Bangladesh. Your expected child will automatically be a citizen, he gets it a passport & takes it with him. The 3 y.o. cannot go to Bangladesh. So what are you going to do with her?

Why do you keep having children with foreigners who cannot & will not support you & these kids, and you cannot support them either? Obviously, something is wrong here that you cannot & will not do anything for your Bangladeshi spouse. So, you & Kid #2 can go to Bangladesh.

You cant just decide to adopt someone and magically get a VISA. At least here in the US, a judge alone can make that decision based on what is best for the child. My ex husband is trying to get my husband to adopt our son to get out of paying child support. It doesn't work as easily as, snapping our fingers and things get done. You need to see an attorney that is experienced in these matters. I am unsure of UK law.

Your current husband cannot adopt the child. Even if the biological father is illegal nor paying child support.That is not how it works.

Besides adopting a child will not get him a visa.

Do you work and have income?