You are not going to be able to get him into a “top tier” place with the baggage of an OTD sibiling. If you lie to the hanhala about the OTD sibling then once they find out and find out they will, your son will be summarily dismissed and then considered even more unworth of addmission anywhere worthwhile.
None of you are looking at the big picture which is that the huge problem in chinuch is that every place only wants “perfect” families and children. All this system of exclusion is doing is creating more OTD children and more dysfunction.
The good news is that the OTD kids might get a decent education now and make something of themselves now that they are rid of a broken education system.