It could, in theory, be done. But there are two DM judgement hurdles built into the rules as written that you must clear before you can proceed.
Is it the same task?
The Eldritch Knight and the Cleric both have what it takes to cast the spell each on their own. The spell is on each of their spell lists, and that's all the spell scroll item requires for someone to be able to attempt to cast it.
But they are going to use different abilities to do so. Does that make it a different task? Picture it: the cleric is chanting the scroll's words as a prayer for a miracle; the Eldritch Knight is incanting the words as a weave of direct magic. Or maybe in your DM's world, clerical and arcane magic are both the same, just backed by different teachings?
Thus, this hurdle is whether the DM judges that the tasks are actually the same, which is a requirement for helping to work.
Can two people cast one spell?
Even if it's the same task, the working together rules have one more requirement: that it be the sort of task that can benefit from help. Normally, casting a spell is not something that anyone can help you with, so a DM could easily say "no" here.
A more generous DM might rule otherwise for the purpose of scrolls, judging that the spellcasting ability check is to correctly interpret the too-high-level spell, and that this can benefit from help. (Of course, this gets back to the first hurdle: can an arcane-type caster help a priest correctly translate the spell's writing into the correct method of invoking the miracle? That does seem a stretch.)
Assuming that spellcasting method differences aren't an issue for using the scroll, then a DM might say that help could be given on the spellcasting ability check through the principle of "two heads are better than one." In this case, the help given would be in the form of understanding and preparing to cast the spell correctly, and the casting itself would be done solo after the check-with-help.
Thus, the second hurdle is whether the DM judges spellcasting from a scroll to be a kind of task that can even be done together.
So, it depends on your DM
Ask your DM. Because helping is, by RAW, only permitted on tasks that the DM judges can benefit from working together, this can only be known per-DM.