i think - i think if the first flight is accepted , it would normally accepted by the next and next next airline , it is not normal to reject something unless that is really a very obvious problem stuff , but the first airline dont want to promise you because they dont know if the other airline may suddenly or accidenly did something crazy.

as long as you asked the second airline that said it is up to the first airline , which mean they dont usually reject things from other airline's transit. then you should be alright.

-i think-