My husband has A- blood his full sister has B- blood and his half brother has A+ blood. Is it possible to have one father for all 3 siblings? And what blood type is possible (for father) in order to do this?

Of course they can, it doesn't mean that if you don't have the same blood type as your siblings, your adopted or something. If your parent's blood types differ from each other there is a huge tendency that the sibling's blood types are different from each other.
Yes its possible.

There are 3 "alleles" that make up the blood groups - A, B, O.

A person can be:
AO - and would be type A
AA - and would be type A
BO - and would be type B
BB - and would be type B
AB - and would be type AB
OO - and would be type O

You inherit 1 allele from each parent. Say in this example your mom is type A and your dad is type B. But say your mom's A is the AO (not AA), and your dad's B is the BO (not BB).

You inherited the A from mom and the B from dad giving you AB. Your sister inherited the O from mom and the O from dad giving her the OO.

There are 2 other options. One is something called Bombay phenotype. I wrote about this in biology a few years ago on this entire topic - Serology (and DNA).

Hard to explain, but I'll try. If you have A, you have antigens on your red blood cells that distinguish that type. Same goes with B. You don't have any antigens on the cells with type O. A precursor to the A antigen and also the B antigen is called H. Normally the H will "change" into the A or the B - determined by heredity of the blood type. Sometimes though the H doesn't change and even though someone may really be type AO or BO for example, it would show up as OO on blood tests.



Hope this helps.

Yes, that is possible.
The way I see it, there are eight possible blood types:
AB +/-
A +/-
B +/-
O +/-

The alleles are:
or
(A, B, O)

If the father's alleles are and the mother's are , then they could parent children with , , , or .
Taking one from each parent, could yield any of these four types.

For the RH +/- test, if one parent is Rh+/Rh-, the other Rh-/Rh-, or both parents Rh+/Rh-, then it is possible to parent both Rh+ AND Rh- children. It only takes one Rh+ out of two to render your blood type positive.

I hope I've explained that well, and helped you.
If you would like further explanation, or any help with anything else, just ask.

Thank you very much for your help!