Edit: Did your wife submit in October or March? Cos you wrote elsewhere that she submitted in October 2018.You're on a good track, some January applicants are still waiting for file transfer, as said medical request takes 5-7 months, but looks like you'll get it earlier. However, you can apply for a visit visa, there's no harm in trying though there's a high chance of refusal but whatever the decision may be, It doesn't affect your sponsorship application. Just provide enough proof of ties to Nigeria.